J Autism Dev Disord DOI 10.1007/s10803-014-2235-2

ORIGINAL PAPER

Feasibility and Effectiveness of Very Early Intervention for Infants At-Risk for Autism Spectrum Disorder: A Systematic Review Jessica Bradshaw • Amanda Mossman Steiner Grace Gengoux • Lynn Kern Koegel

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Ó Springer Science+Business Media New York 2014

Abstract Early detection methods for autism spectrum disorder (ASD) in infancy are rapidly advancing, yet the development of interventions for infants under two years with or at-risk for ASD remains limited. In order to guide research and practice, this paper systematically reviewed studies investigating interventions for infants under 24 months with or at-risk for ASD. Nine studies were identified and evaluated for: (a) participants, (b) intervention approach (c) experimental design, and (d) outcomes. Studies that collected parent measures reported positive findings for parent acceptability, satisfaction, and improvement in parent implementation of treatment. Infant gains in social-communicative and developmental skills were observed following intervention in most of the reviewed studies, while comparisons with treatment-asusual control groups elucidate the need for further research. These studies highlight the feasibility of very early intervention and provide preliminary evidence that intervention for at-risk infants may be beneficial for infants and parents.

Electronic supplementary material The online version of this article (doi:10.1007/s10803-014-2235-2) contains supplementary material, which is available to authorized users. J. Bradshaw (&)
L. K. Koegel Counseling, Clinical, and School Psychology Department, Koegel Autism Center, Graduate School of Education, University of California, Santa Barbara, CA, USA e-mail: [email protected] A. M. Steiner SIERRA Kids, Sacramento, CA, USA G. Gengoux Department of Psychiatry and Behavioral Sciences, Stanford University School of Medicine, Stanford, CA, USA

Keywords Autism
Early intervention
Infancy
Highrisk infants
Treatment

Introduction Research dedicated to advancing methods for early identification of autism spectrum disorder (ASD) has resulted in evidence of behavioral markers in the first year of life (Chawarska et al. 2013; Elsabbagh et al. 2012; Jones and Klin 2013; Maestro et al. 2002; Shic et al. 2014), the development of clinical autism-specific screeners that begin as early as 12 months (Barbaro and Dissanayake 2013; Kleinman et al. 2008; Robins 2008), and a statement by the American Academy of Pediatrics recommending routine screenings for ASD beginning at 18 months (Johnson and Myers 2007). Early identification of ASD in clinical and research settings necessitates parallel development and investigation of early interventions for infants and toddlers that mitigate, and possibly prevent, impairments associated with ASD (Dawson 2008). In light of empirical research documenting significantly improved outcomes with early intervention for preschool and school-aged children with ASD (Granpeesheh et al. 2009; Rogers et al. 2012; Zachor et al. 2007), there is a critical need for the development of effective early intervention techniques during the first years of life. Developmental and transactional models of ASD emphasize interactive biological and environmental processes that shape early development (Dawson 2008; Elsabbagh and Johnson 2010; Mundy and Neal 2000). Evidence of neuroplasticity and critical periods of development in infancy lend support for the investigation of very early interventions. Effective interventions at the earliest age possible may be able to modify early experiences-effectively altering cortical organization, enhancing learning, and potentially improving

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developmental trajectories (Fox et al. 2010; Johnson 2001; Webb et al. 2014). As such, the present article seeks to review current findings in the development and implementation of treatment for infants with or at-risk for ASD in the first two years of life. Current Approaches to Intervention for Autism in Early Childhood Interventions for children with ASD encompass a wide range of techniques that target an array of behaviors or symptoms. Some of the most common therapies accessed by parents of children with ASD include speech/language therapy, applied behavior analysis (ABA), occupational therapy and sensory integration, as well as medication treatments and special diets (Green et al. 2006; Goin-Kochel et al. 2009; Love et al. 2009). Many community-based intervention services for toddlers first diagnosed with ASD fall under the blanket term ‘‘Early Intervention’’ (e.g., IDEA, Part C, and Birth to Three programs). Early Intervention may consist of a variety of services, some of which are empirically validated while others carry minimal empirical support (Stahmer et al. 2005). Despite the popular use of services with limited empirical support, several evidence-based interventions have been established, eleven of which are recognized as ‘Established Treatments’ by the National Standards Project (National Autism Center 2009). At the time of the National Standards Project, the majority of the established treatments were associated with favorable outcomes for preschoolers, school-age children, and middle-school aged children, with very few interventions suggested for use with children under 2 years of age. While some highly structured interventions based on Applied Behavior Analysis have historically had the strongest research support (Lovaas 1987; Reichow 2012), early behavioral interventions for toddlers with ASD have evolved to incorporate elements from developmental psychology in addition to more ‘‘naturalistic’’ methods, in which the intervention is more child-directed and occurs in the child’s natural environment (Schreibman 2014). Some examples of interventions that combine behavioral, naturalistic, and developmental approaches (also termed Naturalistic Developmental Behavioral Interventions; NDBIs) are the Early Start Denver Model (Rogers and Dawson 2010), Enhanced Milieu Teaching (Kaiser and Hester 1994), and Pivotal Response Treatment (PRT; Koegel and Koegel 2012). Why Intervene So Early? The first 2 years of infant development are marked by rapid change and an explosion of cognitive, language, and social abilities. Beginning at birth, early attentional preferences for social stimuli (Johnson et al. 1991) foster the emergence of

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social communication. This developmental pathway is characterized by mutual gaze and shared positive affect (Parlade et al. 2009), social engagement and parental scaffolding (Bakeman and Adamson 1984), and joint attention and gesture use (Tomasello and Carpenter 2007), which emerge within the first 12 months of life. The second year of life is characterized by an exponential growth of verbal communication (Paul 2007). By the time children with ASD are identified and enrolled in treatment programs between 3 and 5 years (Shattuck et al. 2009), the gap between their abilities and those of typically developing peers has often grown quite wide. This early stage of development prior to age two also marks a critical period with regard to accelerated brain growth and connectivity (Courchesne et al. 2003; Wolff et al. 2012), interactive specialization (Johnson 2001), language learning (Kuhl et al. 2005), and potentially social perception and social development (Dawson 2008; Schultz 2005). After 24 months, neurosynapatic development, including cortical specialization and white matter growth, significantly attenuates, making this age a critical period in development and possibly in the pathogenesis of ASD (Wolff et al. 2012). It is hypothesized that atypical development of social mechanisms, including attention, communication, and reward processing, may persist without intervention and could have consequential effects on the subsequent development of social-communicative abilities (Chevallier et al. 2012; Eyler et al. 2012; Schumann and Amaral 2006). Capturing developmentally delayed behaviors and providing enriched experiences and differential reinforcement in this sensitive period, when neural plasticity is heightened, could have a long-term impact on development. That is, if developmental trajectories for vulnerable infants can be altered when the gap between infants with and without delays is small, long-term outcomes could be significantly improved. Evidence for observable prodromal symptoms of ASD in infancy is mounting, making implementation of intervention in this critical period feasible (Barbaro and Dissanayake 2009; Vismara and Rogers 2008). As mentioned above, symptoms of ASD have been documented in the first year of life (e.g. Chawarska et al. 2013; Elsabbagh et al. 2012; Flanagan et al. 2012; Jones and Klin 2013). Additionally, early screening strategies are being evaluated to enable detection and referral in the first year of life (Bryson et al. 2008) and before the second birthday (Dietz et al. 2006; Reznick et al. 2007; Robins 2008; Wetherby et al. 2008). Further, accumulating studies are documenting that many children can be reliably diagnosed at 18 months of age (Chawarska et al. 2007; Guthrie et al. 2012). This is consistent with parent observations confirming concerning behaviors before age two (Young et al. 2003). Clinical assessments and early screeners can help to identify infants and toddlers who are ‘‘at-risk’’ for ASD based on prodromal behavioral features and might benefit from

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intervention and prevention strategies rather than waiting for the emergence of full diagnostic features (Crais and Watson 2014). In addition to infants who are identified as ‘‘at-risk’’ due to behavioral presentation and screening measures, infant siblings of ASD are also identified as ‘‘atrisk’’ due to genetic contributions to the disorder (Ozonoff et al. 2011). Consequentially, pediatric practices are urged to scrupulously monitor infants, especially at-risk infant siblings, and immediately refer them for intervention upon the observation of developmental red flags (Ozonoff et al. 2011). While early detection techniques are being refined and encouraged, empirically based interventions for infants in this early period before 24 months remain limited. The majority of the existing early intervention research focuses on children with ASD in the preschool years, between 2 and 4 years of age (see Boyd et al. 2010 for review). This is problematic considering that current recommendations suggest initiation of intervention within 60 days following a diagnosis (Maglione et al. 2012). In a comprehensive review of interventions for toddlers with ASD under 36 months, Schertz et al. (2012) identified a total of 20 research studies, with only five studies targeting infants under 2 years of age and only one study of a single infant focused on treatment implementation within the first year of life. Given the unique developmental characteristics of children in the first and second year of life, which may warrant additional specialized modifications to intervention focus and method of delivery even beyond those made for 2- to 3-year-olds, we elected to specifically focus on treatments applied to these very young children for the present review. We focus narrowly on the critical period of birth to 24 months and the specific challenges associated with intervening at this very early age, including developmental modifications necessary for implementation of intervention in the prelinguistic period, and evaluating parent outcomes following intervention. For these very young children there is a clear need to address parental concerns as they arise and provide guidelines for delivery of empirically based interventions (Webb et al. 2014). Furthermore, the complexities of identifying infants under 24 months with or at-risk for ASD are highlighted in this review. The present article reviews available research investigating the feasibility and effectiveness of early interventions for infants under 24 months, when routine ASD screenings are recommended and when enriched experience may have a significant impact on development trajectories. The following critical elements are explored within the available infant intervention research: (a) participant characteristics, (b) intervention approach, (c) experimental design, and (d) infant and parent outcomes. A synthesis of existing evidence is intended to guide and inform practitioners as they develop very early intervention programs for ASD and to stimulate research

efforts that may help to mitigate early signs of ASD in infancy and to improve developmental trajectories for atrisk infants.

Methods This review involved a systematic analysis of studies that focused on interventions for infants with or at-risk for ASD under 24 months of age. In order to provide a comprehensive review of the current state of intervention research for this population, each identified study that met predetermined inclusion criteria was analyzed and summarized in terms of (a) participant characteristics, (b) intervention approach, (c) experimental design, and (e) infant and parent outcomes. More specifically, the summary of participant characteristics included the number of participants in each study, the average age, and participants’ risk for ASD. The intervention approach was evaluated with a synopsis of the empirical and theoretical basis of intervention, parent involvement, length and intensity of treatment, and specific intervention goals and strategies. The summary of outcome included reports on infant-specific developmental, diagnostic, social, and communication outcomes as well as parent measures such as satisfaction, feasibility, and acceptability. Search Procedures A systematic search procedure was used to identify studies for possible inclusion in this review. First, a literature search of the following four electronic databases was conducted for articles published from the beginning dates of the database (1949 was the earliest resulting publication) up to June 2014: PsychINFO, Education Resources Information Center (ERIC), Academic Search Complete, and PubMED. The search only included studies written in English that appeared in peer-reviewed journals. The following combination of search terms was entered into each database: autism or autistic or ASD or PDD* or pervasive developmental disorder AND infant or toddler AND intervention or treatment. Additionally, articles that were published online, ahead of print, were searched for the same key terms from the following publishers: Elsevier, Springer, and Sage. This initial search yielded a total of 2,353 articles across all databases after duplications were removed. The articles were then independently screened by the first (JB) and last (LK) authors for the inclusion criteria, listed below. Inclusion Criteria Each study resulting from the initial search was evaluated for the following pre-determined inclusion criteria:

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1.

2.

3.

Research Design. The study involved systematic, experimentally controlled investigation of a non-pharmacological intervention. Example research designs meeting inclusion criteria were randomized controlled trials, quasi-experimental designs, and single-case designs. Uncontrolled case studies (e.g., N = 1) were excluded from this review. In order to ensure the study was evaluating intervention effectiveness, at least one dependent variable had to be a child outcome measure. Autism Risk Status. All participants in the study were diagnosed with ASD or labeled by the study’s authors as at-risk for developing ASD. There were no restrictions related to the study’s methodology for determining diagnosis of ASD or determination of ‘‘at-risk’’ for ASD. Average Age Less than 24 Months. The study focused on children under 24 months of age. In order to account for studies that included primarily, but not exclusively, children less than 24 months, we included studies where the mean age of participants was \24.0 months at the start of intervention.

In order to ensure the accuracy of the systematic search, the first and last authors both independently completed the search and made an initial determination as to whether each study met inclusion criteria. The articles identified by each author were then compared for reliability. Reliability was calculated using percent agreement on the studies each author positively identified as meeting inclusion criteria. This resulted in eight agreements and one disagreement, yielding an overall agreement of 89 %. The one disagreement was based on the Research Design criteria for a study that utilized a quasi-experimental design. Through discussion it was ultimately decided that a quasi-experimental design with a post-test only control group was sufficient to be included in this review. A final total of nine studies met all the inclusion criteria. Coding After the list of included studies was agreed upon, the first and last authors independently extracted information and answered 10 questions related to the four broad categories used to evaluate each study (see Appendix): (a) participant characteristics, (b) intervention approach, (c) experimental design (d) outcomes. Participant characteristics The number of total participants in each study, the age range, and the mean age of participants were collected from each study. The total number of participants was reported for single-case designs and the number of participants in each group was reported for group designs. The age range and mean age

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were reported across all participants for both single-case and group design studies. The age range and mean age were computed for single-case designs in which the age of each participant was reported individually. Additionally, the method in which each study classified its participants as either ‘‘at-risk’’ for ASD or diagnosed with ASD was summarized. Intervention approach Details regarding the intervention approach used by each study included the empirical and theoretical basis, the length and intensity, and goals and strategies. The name and theoretical basis of each intervention was extracted from the description of the intervention. For any studies that did not thoroughly explain a theoretical basis, relevant references cited in that article were reviewed to identify the theoretical foundation. Additionally, it was determined whether the intervention was primarily parent-mediated, clinician-directed, or a combination of both. The length and intensity of each intervention was reported in terms of number of individual sessions over a set period of time. Where possible, the length of each session was also included. If the intervention included group sessions or playgroups, this was indicated as well. The intervention goal(s) of each study referred to how the authors described the overall goal of their treatment. Intervention strategies referred to specific strategies listed by the author that were used or taught in order to meet the intervention goals. Experimental design The type of experimental design used to evaluate effectiveness and/or feasibility of the intervention was reported. Outcomes Intervention outcomes for each study were collected for both infants and parents. This included observed changes in infant measures following the intervention as well as any parent measures that were collected, such as fidelity of implementation or satisfaction. Reliability Coding reliability was calculated for all nine studies in order to ensure accuracy in the summary of studies and to provide a measure of inter-rater agreement on data extraction and analysis. There were 90 items on which there could be agreement or disagreement (i.e., 9 studies with 10 questions per study). Reliability was determined by calculating percent agreement across all nine studies. Agreement was obtained on 80 of the 90 possible items yielding 80 % agreement. In the instances in which there

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was disagreement on any of the items, the items were discussed until consensus was obtained. The final summary was then checked by the co-authors for accuracy. The results are presented in Tables 1 and 2 and the four broad domains are further addressed below.

Schertz and Odom 2007), Pervasive Developmental Disorders Screening Test-II (PDD-ST-II; Schertz and Odom 2007; Siegel 2001), Systematic Observation of Red Flags of ASD (SORF; Wetherby and Woods 2002, 2006), and the Screening Tool for Autism in Two-Year Olds (STAT; Stone et al. 2004; Carter et al. 2011), .

Results

Intervention Approach

Participant Characteristics

Empirical and Theoretical Basis

The nine studies included a total of 353 participants between 4 and 30 months of age. This included 150 infants in the experimental treatment condition and 203 control infants who were either typically developing or received ‘‘treatment-as-usual’’ (TAU). Three studies investigated intervention for participants in the first year of life, between 4 and 12 months (Green et al. 2013; Koegel et al. 2013; Steiner et al. 2013), while six studies intervened with infants primarily in the second year of life, (Carter et al. 2011; Dawson et al. 2010; Drew et al. 2002; Rogers et al. 2012; Schertz and Odom 2007; Wetherby and Woods 2006). The latter six studies that focused on infants with mean age \24 months contributed the majority of treatment participants (N = 137 in the treatment condition) while the former three studies were relatively small and in total reported treatment effects for 13 infants. All studies required that participants be either at-risk for ASD (‘‘at-risk’’ due to behavioral symptoms of ASD or being a sibling of a child with ASD) or diagnosed with ASD prior to participating in the intervention. Three general approaches were used to determine eligibility based on ASD diagnosis or risk status: (1) inclusion of any infant sibling of a child with autism, regardless of behavioral profile (Green et al. 2013; Steiner et al. 2013), (2) expert clinical concern for ASD based on autism screeners or behavioral assessments (Carter et al. 2011; Koegel et al. 2013; Rogers et al. 2012; Schertz and Odom 2007), and (3) clinical or provisional clinical diagnosis of ASD (Dawson et al. 2010; Drew et al. 2002; Wetherby and Woods 2006). Assessment procedures were aimed at ascertaining early symptoms of ASD, and often used multiple sources. These assessments included systematic behavioral observation (Drew et al. 2002; Koegel et al. 2013), Autism Diagnostic Observation Schedule—Toddler Module (ADOS-T, Lord et al. 2012; Rogers et al. 2012), Autism Diagnostic Interview—Revised (ADI-R) and Toddler Autism Diagnostic Interview (Dawson et al. 2010; Drew et al. 2002; Lord et al. 1994), Childhood Autism Rating Scale (CARS; Schertz and Odom 2007; Schopler et al. 1988), Infant Social Communication Questionnaire (ISCQ; Schertz, unpublished; Schertz and Odom 2007), Modified Checklist for Autism in Toddlers (MCHAT; Robins et al. 2001;

Most of the reviewed studies adapted intervention models that had been previously applied for preschool-aged children. Pivotal Response Treatment (Koegel et al. 2013; Steiner et al. 2013), Early Start Denver Model (ESDM; Dawson et al. 2010; Rogers et al. 2012), and Hanen’s More Than Words (HMTW; Carter et al. 2011) have all been researched for use with older children. All authors reported that treatment procedures and targets were modified to be developmentally appropriate for infants under the age of two. The studies by Green et al. (2013), Drew et al. (2002), Schertz and Odom (2007), and Wetherby and Woods (2006) represent the first investigation of the experimental intervention not previously studied with older populations. PRT and ESDM were both reported to be founded in developmental and behavioral theories, with social motivation being emphasized in PRT while ESDM stressed a relationshipbased approach. The Early Social Interaction Project (ESI; Wetherby and Woods 2006) and HMTW both described a family centered and routine-based approach as key elements to their intervention. The Social-pragmatic joint attention parent-training program (Drew et al. 2002) utilizes both developmental and behavioral approaches to teach joint attention. Schertz and Odom (2007) described the Joint Attention Mediated Learning (JAML) intervention as a parent-mediated and family centered approach focusing on the developmental foundations of joint attention. The ‘‘Intervention in BASIS’’ (iBASIS) program (Green et al. 2013) highlighted attachment theory and the importance of parent-infant synchrony. Additionally, five out of the nine reviewed studies reported using a manualized intervention (Dawson et al. 2010; Green et al. 2013; Rogers et al. 2012; Schertz and Odom 2007; Steiner et al. 2013). Parent Involvement Nearly all interventions used parent-mediated procedures. That is, parents were taught specific intervention procedures during treatment sessions and were expected to implement them with their child during and outside of the sessions. Methods in which parents were taught intervention strategies involved didactic sessions about treatment techniques in addition to a ‘‘practice-with-feedback’’

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J Autism Dev Disord Table 1 Description of reviewed studies Study

Carter et al. 2011

Participants

Intervention approach

Experimental design

N and age

Risk determinants or diagnosis of ASD

Empirical and theoretical basis

Length and intensity

Intervention goals and strategies

N = 32 (intervention group) and N = 30 (control group);

– Symptoms of ASD

Hanen’s More Than Words Program (HMTW)

8 group and 3 individual sessions over 3.5 months

Goal: Increase child communication using everyday routines

20-h/week over 2 years

Goal: Improve developmental outcomes

15-24 months (M = 20)

– Expert clinical judgment of ASD

– Socialinteractionist theory – Parentmediated

Strategies: Video feedback; responding to child’s communicative attempts; following child’s lead; joint action routines; use of books to elicit and reward communication; scaffolding peer play dates; visual supports

Randomized controlled trial with treatmentas-usual control group

– Familycentered – Routine-based Dawson et al. 2010

N = 24 (intervention group) and N = 24 (control group); 18-30 months (M = 23.1 intervention group; M = 23.9 control group)

– Clinical diagnosis of ASD or PDD-NOS

Early Start Denver Model (ESDM)

Strategies: Interpersonal exchange and positive affect; shared engagement; adult responsivity and sensitivity to child cues; focus on verbal and nonverbal communication; behavioral principles (operant conditioning, shaping and chaining); plan individualization

– Developmental and behavioral theory – Relationshipbased – Therapist and parentdelivered

Drew et al. 2002

N = 12 (intervention group) and N = 12 (control group); Under 24 months (M = 22.6)

– Clinical diagnosis of ASD

Social-pragmatic joint attention focused parent training program

One 3-h session every 6 weeks over 12 months

Goal: Enhance communication skills

12 sessions over 5 months

Goal: Improve the quality of parentinfant interactions and increase parent-infant synchrony

– Developmental and behavioral theory

Strategies: Behavior management; joint action routines; teaching joint attention behaviors (mirror games, pointing, following points, gaze switching game); increase mutual enjoyment; exaggerated prosody; repetitive paraphrasing

Randomized controlled trial with a treatment-asusual control group

Randomized controlled trial with a treatment-asusual control group

– Parentmediated Green et al. 2013

N = 7 (case series group) and N = 70 (comparison groups);

– Sibling with ASD

Intervention in BASIS (iBASIS) – Developmental and attachment theory

8–10 months (M = 8)

Strategies: Use of video aides; maternal sensitive and contingent responding; affect matching; reciprocal vocalization

– Parent-infant synchrony Koegel et al. 2013

N = 3; 4–9 months (M = 6)

– Symptoms of ASD – Expert clinical concern for ASD

Pivotal Response Treatment (PRT) – Behavioral and developmental theory – Social motivation hypothesis

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1 h/week for 4-11 weeks

Goal: Increase motivation to engage in social interaction Strategies: Use of infant-preferred activities; task variation; interspersal of preferred and neutral activities; reinforcement

Case series with a high-risk and low-risk control group

Multiple baseline design across participants

J Autism Dev Disord Table 1 continued Study

Rogers et al. 2012

Participants

Intervention approach

Experimental design

N and age

Risk determinants or diagnosis of ASD

Empirical and theoretical basis

Length and intensity

Intervention goals and strategies

N = 49 (intervention group) and N = 49 (control group);

– Symptoms of ASD

ParentImplemented Early Start Denver Model (P-ESDM)

1 h/week for 12 weeks

Goal: Improve social, communicative, and developmental outcomes

12–24 Months (M = 21)

– Expert clinical judgment of ASD

Strategies: Increase child attention and motivation; use of sensory social routines; joint activity routines; use of antecedent-behavior-consequence relationships; use of prompting, shaping, fading, and functional behavior assessment

– Developmental and behavioral theory – Relationshipbased

Randomized controlled trial with treatmentas-usual control group

– Parentmediated Schertz and Odom 2007

N = 3; 20–28 months (M = 23.7)

– Symptoms of ASD – Positive screen for ASD

Joint Attention Mediated Learning (JAML)

1-2 sessions/ week over 9-26 weeks

Goal: Promote joint attention

Ten 1-h sessions over 3 months

Goal: Increase functional communication and social motivation

– Developmental theory

Strategies: Engage in face-to-face interactive games; turn-taking activities; respond to join attention; initiating joint attention activities

Multiple baseline design across participants

– Mediated learning – Familycentered – Parentmediated Steiner et al. 2013

N = 3; 12 months (M = 12)

– Sibling with ASD

Pivotal Response Treatment (PRT)

Strategies: Following the child’s lead; providing clear prompts; interspersal of maintenance and acquisition tasks; use of immediate, contingent, and natural reinforcement; reinforcement of attempts

– Behavioral and developmental theory – Social motivation hypothesis Wetherby and Woods 2006

N = 17 (intervention group); 12–24 months (M = 18) N = 18 (3rd year contrast group); 25–36 months (M = 31)

– Provisional clinical diagnosis of ASD

Early Social Interaction Project (ESI) – Developmental theory – Parentmediated – Familycentered

2 individual sessions/week and 9 playgroup sessions over 12 months

Goal: Improve social communication in the context of family routines Strategies: Goal individualization; environmental arrangement; waiting; natural reinforcers; balanced turntaking; modeling; contingent imitation; requesting imitation; time delay

Multiple baseline design across participants

Quasiexperimental design with a post-treatment contrast group

– Routine-based

model in which parents and their infant practiced the intervention while a clinician provided feedback about implementation. Only one study was therapist-delivered, but incorporated a parent-training component (Dawson et al. 2010). Parent education took place primarily in the natural environment (i.e., the home) for seven of the nine studies (Carter, et al. 2011; Dawson et al. 2010; Drew et al. 2002; Green et al. 2013; Koegel et al. 2013; Schertz and

Odom 2007; Wetherby and Woods 2006). Intervention occurred primarily in a university clinic setting for the two remaining studies (Rogers et al. 2012; Steiner et al. 2013). Length and Intensity Length of treatment ranged from 4 weeks to 2 years and all but one intervention were low-intensity, totaling no more

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J Autism Dev Disord Table 2 Infant and parent outcomes Study

Infant outcome

Parent outcome

Carter et al. 2011

No main effects of treatment were observed for any child outcome variables. A medium effect size for child social communication was found for both the HMTW and treatment-as-usual (TAU) groups. Children in the HMTW group who exhibited less Child Object Interest prior to intervention achieved greater gains in initiating joint attention, initiating behavioral requests, intentional communication, and parent-reported nonverbal communication

Medium-to-large, but statistically insignificant, improvements in parent responsivity were observed following intervention

Dawson et al. 2010

Improvement in nonverbal cognitive skills significantly greater than baseline assessment and the TAU group after 1 year of intervention. After 2 years of intervention, the ESDM group showed significantly greater improvements in receptive and expressive language as well as parent-reported communication, daily living skills, and motor skills. No significant group differences in autism severity were observed, but toddlers in the ESDM group were more likely to have improved diagnostic status

No parent outcomes were reported

Drew et al. 2002

Significantly more children in the Parent training group moved from being minimally verbal to having single word or phrase speech than in the TAU group. The Parent training group had marginally higher language comprehension than the TAU group. There were no group differences in nonverbal IQ, words, gestures, or symptom severity

There were no group differences in parent-stress

Green et al. 2013

Preliminary results suggest improvement in infant liveliness for both treatment and control groups, but greater improvement in treatment group

Koegel et al. 2013

Rapid increases in social engagement for all participants following initiation of the intervention. Social engagement was defined as increased happiness, interest, and response to name, as well as decreased eye contact avoidance during parent-infant interactions. These gains were maintained at a two and six month follow-up

High session attendance and reports on parent satisfaction questionnaires suggest overall feasibility and acceptability. Preliminary results show that all but one mother who exhibited low synchrony behaviors, i.e. nondirectiveness and sensitive responsiveness, improved on these measures following intervention All parents learned to correctly implement the intervention procedures and met the Fidelity of Implementation criterion during all intervention sessions

Rogers et al., 2012

Both groups (P-ESDM and TAU) made significant gains in rates of acquisition of developmental skills and reduction of core symptoms of ASD following the 12-week intervention. No group differences on any primary child outcome variables were found. Developmental and diagnostic improvements were associated with more intervention hours and younger age at the start of intervention. Children in the TAU group received a greater number of intervention hours. Contrary to the authors’ hypothesis, social orienting and imitation did not moderate the child effects of P-ESDM.

Parents in both P-ESDM and TAU groups showed significant improvement in their use of ESDM interaction skills in the 12-week period. Although these groups did not significantly differ in their acquisition of the ESDM treatment procedures, the P-ESDM group exhibited a larger effect size than the TAU group following intervention. Further, parents in the P-ESDM group reported a stronger working alliance with their therapist than parents in the TAU group

Higher parent P-ESDM fidelity scores at the start of the study were significantly related to milder ASD symptoms and higher developmental scores Schertz and Odom 2007

All participants improved above baseline in focusing on the parents’ face, turn-taking, responding to parents’ joint attention overtures, and initiating joint attention encounters. One participant only slightly improved on the two joint attention measures

Parent satisfaction with their child’s progress following intervention was high for two out of three parents and all parents improved confidence in their ability to support child interactions. Parent participation was high for all parents and fidelity of implementation was high for two out of three parents

Steiner et al. 2013

All participants demonstrated rapid increases in frequency of communication with their parent following the start of intervention. These gains maintained at post-treatment. Followup developmental testing at 36 months showed decreases in autism symptomology

Following intervention, all parents demonstrated independent, correct implementation of intervention procedures both with and without a clinician present. Additionally, all parents reported high overall satisfaction with the intervention

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J Autism Dev Disord Table 2 continued Study

Infant outcome

Parent outcome

Wetherby and Woods 2006

After one year of treatment, children in the intervention group exhibited significant improvements in all reported measures of social-communication, except for shared positive affect and number of gaze shifts. The intervention group also exhibited superior skills in social signals, rate of communicating, communicative functions, and understanding compared to the third year contrast group

None reported

than 2 h of intervention per week. All treatment programs included the expectation that parents would frequently implement the intervention strategies throughout the week and integrate them into daily activities. Dawson et al. (2010) was the only study to collect data on the amount of time the intervention procedures were implemented by the parents outside of the intervention sessions (an average of 16.3 h per week). Intervention Goals and Strategies Most of the reviewed studies discussed behavioral principles as a foundational element of intervention (Carter et al. 2011; Dawson et al. 2010; Drew et al. 2002; Koegel et al. 2013; Rogers et al. 2012; Steiner et al. 2013; Wetherby and Woods 2006). Behavioral components that provided a framework for intervention included: providing a learning opportunity (antecedent), waiting for the child to respond (behavior), and delivering appropriate reinforcement (consequence). Further, all interventions used naturalistic approaches such that the infant’s daily routines, natural interests, or preferred activities were infused into treatment procedures. Goals for intervention fit generally under the broad developmental area of social-communication, constituting one of the two core areas of ASD in the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5; American Psychiatric Association 2013). All interventions embraced a developmental framework by adapting treatment targets and intervention strategies to be developmentally appropriate for the age of the sample. For example, one of the treatment goals for 6-9-month-olds was to increase social engagement, namely positive affect and social interest (Koegel et al. 2013) while an intervention program for 20-month-old toddlers targeted receptive and expressive verbal communication (Carter et al. 2011). For this reason, intervention procedures are summarized below in two developmental stages: the first and second years of life. First Year: 4–12 Months Green et al. (2013) developed the ‘Intervention in BASIS’ (iBASIS) program based on

autism-specific intervention strategies previously established in the Preschool Autism Communication Trial (PACT; Green et al. 2010). The primary aim of the intervention was to increase parent-infant synchrony while also addressing emerging symptoms of ASD in 8–10 month-old infants. Improvements in parent-infant synchrony were hypothesized to lead to improvements in child dyadic communication and reductions in ASD symptoms. Koegel et al. (2013) also provided an intervention designed to modify parent-infant interactions for prelinguistic infants. Using PRT (Koegel and Koegel 2012), this brief intervention program aimed to increase infants’ motivation to engage in social interaction. Specifically, goals were to increase eye contact, happiness, and interest during parentinfant interactions. Similarly, in an intervention program for 12-month-old infants (Steiner et al. 2013), procedures and target behaviors of PRT were modified for use with infants. Traditionally, PRT has been studied with preschool and school-aged children where the focus of intervention is initially verbal communication (Koegel et al. 1999). These treatment targets were adapted for 12-month-olds to include verbal (vocalizations, word approximations), nonverbal (gestures, pointing, giving, showing, and communicative reaching), and coordinated social communicative behaviors (communication involving multiple verbal and/ or nonverbal behaviors). Second Year: 13–30 Months Six of the reviewed research studies investigated the effectiveness of interventions for infants with a mean age between 13 and 24 months of age (range 13–30 months). The ESDM (Dawson et al. 2010) is a comprehensive developmental and behavioral treatment model that focuses on the use of naturalistic methods for supporting young child development. In addition to traditional ESDM, which focused on improving developmental outcomes through an intensive therapist-delivered program, parent-implemented ESDM (P-ESDM; Rogers et al. 2012) focused on teaching parents strategies for engaging in childcentered responsive interactions. Both intervention models targeted the following child behaviors: attention, motivation, social engagement in joint activity routines, verbal and nonverbal communication, imitation, and joint attention.

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The Early Social Interaction (ESI) Project (Wetherby and Woods 2006) aimed to teach parents to increase social communication in their toddler using strategies based on behavioral principles that included natural reinforcement, time delay, modeling, turn-taking, and imitation. Specific target behaviors differed for each toddler based on individual goals and parental input, but broadly related to social communication skills. The HMTW program (Carter et al. 2011) emphasized the use of everyday routines to target improvements in social communication. The intervention aimed to teach parents to increase their responsivity to child communicative attempts, provide rewards, follow the child’s lead, and build joint action routines. HMTW target behaviors included improving two-way interactions and increasing expressive and receptive communicative abilities. Drew et al. (2002) used a social-pragmatic joint attention focused parent-training program to promote joint action routines and teach children with ASD joint attention behaviors. Language-learning was promoted through the use of exaggerated prosody and repetitive phrasing and behavioral management strategies were also taught to parents. Schertz and Odom (2007) also employed a joint attention focused intervention, but rather than explicitly teaching joint attention using a behavioral framework, the JAML program structures parent–child interactions in a way that promotes joint attention. Experimental Design Overall, effects of intervention were measured using preand post-treatment behavioral assessments. Four studies (Carter et al. 2011; Dawson et al. 2010; Drew et al. 2002; Rogers et al. 2012) employed randomized controlled trials with a TAU control group. Wetherby and Woods (2006) used a quasi-experimental design in which post-intervention outcomes were compared to a TAU control group, however the control group was not available for comparison at preintervention. A case series design in which a small sample of treatment participants was compared to both an at-risk nonintervention control group as well as a low-risk non-intervention control group was reported in Green et al. (2013). Koegel et al. (2013), Schertz and Odom (2007), and Steiner et al. (2013) used a multiple baseline design in which change was measured through repeated observations prior to, during, and after the intervention. Intervention Outcome Feasibility and Acceptability Parent-perceived acceptability and feasibility are especially important components for interventions with infants and

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toddlers when the parent is the primary interventionist. Most studies reported very high satisfaction with the intervention on satisfaction questionnaires (Carter et al. 2011; Green et al. 2013; Schertz and Odom 2007; Steiner et al. 2013), while Rogers et al. (2012) reported stronger working alliances between parents and therapists in the P-ESDM group over the comparison TAU group. Additionally, most studies evaluated training fidelity for parent performance in adhering to intervention procedures and correctly implementing techniques. Results of fidelity of implementation measures showed that parents improved in their ability to implement the specific intervention strategies taught during intervention (Koegel et al. 2013; Rogers et al. 2012; Schertz and Odom 2007; Steiner et al. 2013). Additionally, some studies monitored treatment integrity by collecting fidelity of implementation measures for clinicians (Carter et al. 2011; Dawson et al. 2010; Rogers et al. 2012; Wetherby and Woods 2006). These methods included completing self-assessment checklists and behavioral coding of videotaped intervention sessions. However, one study that compared fidelity of implementation of parents in the active treatment condition to parents in the control group found that parents in the TAU group were equally as skilled at implementing the intervention procedures despite never being taught the intervention (Rogers et al. 2012). Developmental Outcome Assessments of behavioral functioning and developmental ability were conducted pre- and post-treatment for five of the nine studies (Dawson et al. 2010; Drew et al. 2002; Green et al. 2013; Rogers et al. 2012; Steiner et al. 2013). These measures included the Griffiths Scale of Infant Development, MacArthur Communicative Development Inventories, Mullen Scales of Early Learning, and Vineland Adaptive Behavior Scales. Three studies observed within-group gains in cognitive abilities (Dawson et al. 2010; Rogers, et al. 2012; Steiner et al. 2013). Additionally, Dawson et al. (2010) reported gains in cognitive skills and adaptive behavior greater than that of the TAU control group, while Rogers et al. (2012) did not observe significant between-group differences in developmental outcome following the brief 12-week intervention. Diagnostic outcome The effect of intervention on autism symptomology was assessed through two autism-specific evaluations for infants and toddlers, the ADOS-T and the Autism Observation Scale for Infants (AOSI; Bryson et al. 2008). Although intervention for infants and toddlers with or atrisk for ASD older than 12 months appeared to lessen

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autism symptom severity, again it was reported that these improvements were not significantly different than improvements of toddlers in the TAU control group (Dawson et al. 2010; Drew et al. 2002; Rogers et al. 2012). Furthermore, measurement of autism symptomology earlier in life using the AOSI and a visual disengagement task between 8 and 10 months of age revealed no obvious effects of intervention (Green et al. 2013). Social-Communication Outcome Intervention effectiveness for the youngest group of infants was measured primarily through change in infant social engagement during parent-infant interactions. Intervention for infants in the first year of life demonstrated improvements in infant positive affect, eye contact, and response to name (Koegel et al. 2013), as well as preliminary findings indicating increases in infant liveliness (Green et al. 2013). Additionally, gains in emerging communication were captured with increase in the use of eye contact, vocalizations, and/or gestures during parent-infant interactions (Steiner et al. 2013), Infant functional communication was among the primary outcome measures for infants older than 12 months. Observed gains included improved performance on the expressive and receptive language (Dawson et al. 2010; Drew et al. 2002; Rogers et al. 2012; Wetherby and Woods 2006), and an increase in behaviors related to joint attention (Carter et al. 2011; Schertz and Odom 2007; Wetherby and Woods 2006). However, gains in social-communication were only greater than the TAU group for children enrolled in 2 years of ESDM (Dawson et al. 2010). Moderators of Outcome Two studies included moderator variables to uncover the effects of specific child and intervention characteristics on child outcomes. Rogers et al. (2012) identified several variables leading to improved outcome for all toddlers, regardless of treatment condition. In particular, nonsocial orienting prior to intervention predicted developmental ability and lower ADOS Social Affect scores, while social orienting was found to predict decreases in the ADOS Restricted and Repetitive Behavior at outcome. This study also revealed significant relationships between both age at the start of treatment and the number of intervention hours. That is, toddlers who were younger and received more hours of intervention demonstrated enhanced developmental gains and greater decreases in autism symptomology. Finally, Carter et al. (2011) identified decreased object interest as a moderator for facilitated growth in communication for the HMTW group.

Discussion Treatments for infants with or at-risk for ASD in the first 2 years of life are still emerging and at the time of this review, only nine identified studies have investigated the feasibility and effectiveness of very early intervention. Three studies examined intervention for infants in the first year, and six studies focused on infants in the second year of life. There was a mix of experimental designs including four randomized controlled trials (RCTs), three multiple baseline designs, and two quasi-experimental designs. The multiple baseline designs demonstrated improvement in infant social engagement and communication behaviors following intervention (Koegel et al. 2013; Schertz and Odom 2007; Steiner et al. 2013), while the RCTs had mixed findings regarding enhanced effectiveness over the TAU comparison group (Carter et al. 2011; Dawson et al. 2010; Drew et al., 2002; Rogers et al., 2012). The quasiexperimental designs documented feasibility and provided preliminary support for treatment effects on infant behavior, including increased infant liveliness (Green et al. 2013) and improved social communication (Wetherby and Woods 2006). Overall, the studies reviewed provide a foundation for the further development and investigation of interventions for infants and toddlers under 2 years of age who are at-risk for, or diagnosed with, ASD. These studies also highlight several issues in need of continued exploration, including effectiveness of intervention for reducing symptoms of ASD in infancy, impact of intervention on parent stress and fidelity of implementation, and reliable strategies for identifying at-risk infants. Treatment Effectiveness Empirical evidence for the effects of intervention on infant and toddler social and communicative development presented in this review is encouraging, but demonstrates the need for further research. Most studies demonstrated some improvement in verbal and nonverbal communication, social engagement, and autism symptomology from pre- to post-intervention, providing preliminary evidence supporting the effectiveness of very early intervention. However, two out of the four studies employing an RCT with a TAU control group found that the target interventions (P-ESDM and HMTW) did not result in gains significantly greater than the TAU comparison group. Notably, the only study to successfully demonstrate efficacy of a specific intervention (Dawson et al. 2010) was the most intensive intervention and the only one to utilize both cliniciandelivered treatment methods and parent training. This stresses the need for more rigorous investigation of the key ingredients in intervention for this very young population. Interestingly, Rogers et al. (2012) note that the TAU group

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in fact received a greater number of intervention hours than the P-ESDM group, and that the number of hours positively predicted improvement on child outcome measures. The authors also highlight the likelihood that the TAU group received a parent education program that resembled many aspects of their own P-ESDM program, calling to question the true difference in service delivery between the two groups. As a final note, the authors question the suitability of some measures (e.g. ADOS, Vineland) in evaluating short-term changes following a 12-week intervention. These questions regarding validity of the TAU and selection of appropriate outcome measures are critical considerations for accurately evaluating the effectiveness of early interventions. It would be prudent for future research to weigh the benefits of conducting an RCT using a TAU control group design against the challenges when limited information is available about the nature of these community treatments. For example, it may be more advantageous to directly compare established treatments that can be delivered in a standardized way at a specified intensity in order to evaluate the unique contributions of each treatment approach. This experimental design may be more effective in understanding the effects of treatment. Multiple baseline design studies begin to allow for analysis of treatment effectiveness while controlling for maturation, an especially critical threat to validity in research with young infants and toddlers. However, this approach is complicated by the heterogeneity of typical development and the documented trends of some high-risk siblings who resolve developmental delays quickly and without the need for intervention (Landa et al. 2007). Inherent weaknesses of multiple baseline designs also include questions of generalizability and specific treatment efficacy without a comparison group. Recommendations for optimal intervention research designs include multisite RCTs that control for several variables including intensity and length of treatment, active ingredients of treatment, and both short and long-term effects on child outcome (Kasari 2002). Exploration of moderator variables associated with outcome data can provide critical information about factors influencing the effectiveness of intervention. For example, HMTW was documented to be more effective with children with less interest in objects, whereas children who had a high interest in objects were less amenable to the treatment program (Carter et al. 2011). Identifying behavioral profiles that match particular intervention methods for children with ASD has long been a topic of interest (e.g. Sherer and Schreibman 2005; Stahmer et al. 2011), and infant intervention research could benefit from identifying subgroups that might differentially benefit from specific treatment strategies.

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Additional moderators for treatment identified in the studies reviewed include the infant’s age and the intensity of intervention. Younger children and those who received more hours of intervention seemed to benefit more from early intervention (Rogers et al. 2012). Intriguingly, no studies reported moderating effects of cognitive ability or verbal communication, despite other studies reporting these factors in early childhood are predictors of positive outcome later in life (e.g., Billstedt et al. 2007). These and other potential moderators should continue to be explored in future research. Most intervention programs for children with ASD focus on increasing social-communication and decreasing problem behaviors, assuming that poor socialcommunicative abilities may have cascading long-term effects on a variety of areas including academic success, mental health, and independent living. Indeed, higher cognitive ability and early-onset verbal communication in childhood are among the best-known prognostic indicators for improved outcome (Billstedt et al. 2007). For infants with prodromal symptoms of ASD, however, pivotal behaviors that will maximally improve outcomes are not well understood. Long-term prognostic factors for infants at-risk for ASD should be investigated with an emphasis on improved functioning for the individual as well as the family system. Recent research on long-term ASD outcome has begun to scrutinize the meaning of ‘‘positive outcome’’ for the individuals and their families (e.g., Henninger and Taylor 2013). Similar rigor should be applied in defining positive outcome for infants, which will then directly influence the identification of target behaviors. The current studies have begun to tackle this issue by capitalizing on family therapist collaborative decision-making processes (e.g., Wetherby and Woods 2006) and pivotal areas, such as motivation (e.g., Koegel et al. 2013), in goal development. Feasibility Establishing feasibility was a key objective in all reviewed studies. Feasibility is an important component of intervention models as it provides preliminary support for widescale dissemination and yields information about acceptability for clinicians and parents (Smith et al. 2007). Some of the reviewed studies used measures of parent satisfaction, parent involvement, and fidelity of implementation to address issues of feasibility. Despite emphasis on parental responsibility to implement the intervention throughout daily routines, families reported very high satisfaction, high involvement in treatment sessions, and enjoyment of the intervention. In fact, Estes et al. (2013) reported in a later study that P-ESDM parents (Rogers et al. 2012) experienced significantly less stress than the TAU control group, after controlling for autism social severity and

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baseline levels of stress. This finding is consistent with this group also reporting stronger working alliances with therapists. Furthermore, Schertz and Odom (2007) used qualitative methods to examine parent perspectives on the intervention, revealing a relation between increased autism severity, slower progress in treatment, and lower parent fidelity of implementation. Research suggests that generalization of learned behaviors and maintenance of gains for children with ASD largely depends on the persistent and consistent implementation of naturalistic behavioral procedures, making fidelity of implementation an important measure of feasibility, and possibly child outcome (Kashinath et al. 2006; National Research Council 2001; Rocha et al. 2007). The studies reviewed here demonstrated the effectiveness of teaching parents to implement intervention techniques, possibly suggesting that this type of dissemination model may be appropriate and implementable by some parents of at-risk infants. Interestingly, Rogers et al. (2012) reported that the TAU control group met fidelity of implementation to the same degree as the P-ESDM group. The authors speculate that this was due to the community TAU parents learning similar skills to the P-ESDM parents, and the community TAU infants receiving significantly more hours of intervention. Furthermore, fidelity of implementation (FOI) scores were quite high prior to onset of intervention, suggesting a sample bias that could contribute to the lack of FOI difference between the groups. Participants were highly educated, 80 % of parents had received at least some college education, and half of the participants had an older sibling with ASD or another developmental disability. It is then possible that parents had a priori knowledge of common intervention procedures and were already integrating some techniques into routine interactions with their at-risk infant. The challenge of gathering representative participant samples is not unique to this study and is acknowledged as a limitation by the authors. There remains an urgent need to recruit representative samples and identify the effects of such demographic variables on FOI and child outcome. Future research investigating parent FOI and child outcome will help to guide clinical practice. It is also interesting to note that although our search criteria included all delivery modes for intervention, all of the studies that met our inclusion criteria were at least partially parent-mediated. Eight of the nine intervention studies used a parent-mediation model that was very lowintensity, averaging 1–2 h per week. While this is in line with several intervention studies for toddlers with ASD that have demonstrated effectiveness of low-intensity interventions (e.g., Vismara et al. 2009), it is significantly less than the Early Intensive Behavior Intervention (EIBI) model in which 40 h per week of clinician-delivered intervention is recommended (Lovaas 1987). Additionally,

research suggests that intensity of early interventions is positively associated with improved child outcome (Reed et al. 2007), a finding that was replicated by Rogers et al. (2012). Despite the limited number of studies in this review, the research presented here could suggest that a more intensive intervention evaluated over a longer period of time (Dawson et al. 2010) may result in greater gains than 1 h per week of parent-mediated intervention. Future research should consider the possibility that more hours of intervention are needed in order to improve symptoms of ASD in infancy. Early Identification and Prevention One of the greatest difficulties associated with designing research studies to investigate the effectiveness of very early intervention for infants at-risk for ASD is the issue of accurate identification. The reviewed studies used three primary methods to address this challenge. A firm clinical diagnosis or provisional clinical diagnosis of ASD was required for only three studies while four of the remaining studies required participants to exhibit behavior that warranted clinical concern for ASD based on quantifiable behavioral assessment and/or an autism screener. The use of both clinical judgment and behavioral assessment could reflect the concern that currently available diagnostic tools may lack the sensitivity and specificity to serve as the sole determinant of risk for ASD in infancy. Alternatively, two studies assumed a model of prevention and provided intervention to all infants at increased genetic risk for ASD (i.e., younger siblings of children with ASD). However, a large proportion of these children would be expected to have typical developmental trajectories even without any intervention, making evaluation of intervention effects challenging (Ozonoff et al. 2011). These approaches to ascertaining risk for ASD in infancy give rise to the question of whether or not a diagnosis of ASD is necessary to provide intervention. Public health models are increasingly adopting models of preventative care, in which medical professionals note prodromal features and, in an effort to avoid the manifestation of full-scale symptomology, provide the indicated treatment prior to diagnosis (American Academy of Pediatrics 2006). The preliminary, but generally positive, treatment results of the reviewed studies support the further development of prevention models and warrant additional experimentally controlled research designs to establish the effectiveness of behavioral intervention for infants in the first 2 years of life. The data presented here may suggest that intervention beginning as early as 6 months of age could lead to observable improvements in core areas of ASD, at least in the short-term, and if continued research supports these findings, the argument for identifying and

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referring at-risk infants in the first 2 years of life, before ASD is typically diagnosed, is even stronger. Limitations This review paper has several limitations. Due to the limited number of studies on this topic to date, conclusions presented here are based upon a relatively small sample size, especially regarding interventions for infants in the first year of life. It was also necessary to analyze treatments for infants with confirmed diagnosis of ASD along with treatments for infants at-risk for ASD, which makes conclusions from this heterogeneous group more challenging to interpret. It is possible that other relevant findings were excluded based on criteria related to experimental design or publication in English-language peer reviewed journals. Though an effort was made to include studies where the majority of children were under 24 months (mean age did not exceed 24 months), the review did not include studies where only a few participants fell in this age range. Finally, the diverse methodological approaches and varied outcomes measured across studies necessitate additional replication of results to confirm the initial findings for each of these novel treatment applications. While it is premature to make conclusions about differential effects of the treatments reviewed, this review serves as a guide summarizing research efforts to date. Future Directions Prevention and intervention efforts for infants at-risk for ASD in the first 2 years of life are part of a burgeoning trend in the field, with several studies documenting preliminary positive findings. The evidence suggests that parent-mediated treatment programs may improve short-term outcomes for at-risk infants and toddlers, including social engagement and communication, yet additional research is needed in this area (National Autism Center 2009). The heterogeneity of both typically developing infants and those with ASD calls for both acute scientific rigor and careful evaluation and description of presenting symptoms. Experimental design issues, including the use of a TAU control group, potential sample biases, and threats to internal and external validity, must be thoughtfully considered in future research for this population. Research exploring novel methodologies for identifying infants and toddlers who are ‘‘at-risk’’ and for determining appropriate targets for intervention is needed. Family context and cultural variables should also be of primary importance in designing individual treatment plans and delivering parent education. Furthermore, intervention studies should carefully consider moderator variables that may influence differential treatment effectiveness for such a heterogeneous population. Observed child gains and high

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levels of parent satisfaction following intervention are encouraging and long-term outcome studies will enrich our understanding of the effects of receiving intervention during the first 2 years of life. Acknowledgments This study was not directly funded, however conceptualization for this article was aided by a predoctoral fellowship awarded to the first author by the Autism Science Foundation (11-1014). We would like to express our appreciation to all families who continue to dedicate their time to autism research.

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