Preimplantation genetic diagnosis for inherited neurological disorders Ilan Tur-Kaspa, Roohi Jeelani and P. Murali Doraiswamy Abstract | Preimplantation genetic diagnosis (PGD) is an option for couples at risk of having offspring with an inherited debilitating or fatal neurological disorder who wish to conceive a healthy child. PGD has been carried out for conditions with various modes of inheritance, including spinal muscular atrophy, Huntington disease, fragile X syndrome, and chromosomal or mitochondrial disorders, and for susceptibility genes for cancers with nervous system involvement. Most couples at risk of transmitting a genetic mutation would opt for PGD over prenatal testing and possible termination of a pregnancy. The aim of this Perspectives article is to assist neurologists in counselling and treating patients who wish to explore the option of PGD to enable conception of an unaffected child. PGD can be accomplished for most disorders in which the genetic basis is known, and we argue that it is time for clinicians and neurological societies to consider the evidence and to formulate guidelines for the responsible integration of PGD into modern preventative neurology. Tur-Kaspa, I. et al. Nat. Rev. Neurol. advance online publication 27 May 2014; doi:10.1038/nrneurol.2014.84

Introduction Common or rare inherited neurological disorders result in impaired nervous system development or abnormal neuromuscular function and neurodegeneration, and are difficult to modify or stop with currently available pharmacotherapies.1–4 The increasing availability of standardized genetic screening panels has led to increased rates of diagnosis of inherited neurological disorders. In turn, genetic screening has helped patients to plan for the future and to improve their outcomes through early intervention or by avoiding harmful drug Competing interests I.T.‑K. is the Medical Director and owner of the Institute for Human Reproduction in Chicago, IL, USA, a private fertility centre that offers advanced infertility and in vitro fertilization treatments, with or without preimplantation genetic diagnosis. P.M.D. has received research grants and/or consultation or speaker fees from Abbvie, Accera, Alzheimer’s Drug Discovery Foundation, Baxter, Cognoptix, Danone, Eli Lilly, Envivo, Genomind, Grifols, Janssen, Lundbeck, Neurocog Trials, Neurontrix, Piramal Healthcare, Shire, Sonexa Therapeutics, Takeda Pharmaceutical Company and Targacept for other projects. He is a shareholder in Sonexa, AdverseEvents, Maxwell Health and Clarimedix, the products of which are not discussed here. R.J. declares no competing interests.

treatment. Genetic testing has also led to greater numbers of at-risk patients seeking options to prevent the onset of disease both for themselves and their offspring. Preimplantation genetic diagnosis (PGD) is a genetic test carried out before gestation begins in the uterus.5–7 Embryos created through in vitro fertilization (IVF) are tested for a known genetic mutation or chromosomal abnormality, and only the unaffected embryos are transferred into the uterus with the aim of producing a healthy child (Figure 1). PGD was first described in 1990 in London8 and Chicago,9 and has been successfully used as a clinical service in the diagnosis of over 200 different diseases, resulting in the birth of thousands of u ­ naffected healthy c­ hildren worldwide.10–15 PGD has been successfully performed for neurological and neuromuscular conditions such as spinal muscular atrophy (autosomal recessive), myotonic dystrophy and Huntington disease (HD; both autosomal dominant), and the X-linked disorders fragile X syndrome and Duchenne muscular dystrophy (DMD; Table 1).6,10–15 PGD has also been carried out for familial Alzheimer disease, mitochondrial dis­ orders, familial spongiform encephalopathy


owing to prion infection, and for cancer susceptibility genes with high penetrance for neurofibromatosis, von Hippel–Lindau syndrome and retinoblastoma, as well as for non-life-threatening conditions such as nonsyndromic deafness (Table 1).11,12,15,18 Preimplantation genetic screening (PGS) can be used to test for ­a neuploidy and ­chromosomal rearrangements. Several societies for reproductive health, along with geneticists and experts in the field, propose that counselling of patients and family members on the possibility of using IVF–PGD to prevent transmission of a genetic mutation or chromo­s omal abnormality to future generations should be an integral part of the standard of care (Box 1).12,14,19–26 Neurological societies have yet to issue formal recommendations on the use of PGD. Such recommendations might be overdue given the growing numbers of patients seeking PGD, often without the knowledge of their primary physician. Interestingly, a 2013 survey of 220 US internists revealed a substantial gap in phys­i cians’ knowledge about PGD—the major­ity (>90%) had never suggested PGD to a patient and felt unqualified to answer patients’ questions about PGD.27 About 60% of intern­ists were uncertain whether or not they could refer patients with neuro­logical dis­orders, such as HD, DMD or familial retino­blastoma, for PGD. 27 Using cystic fibrosis as an example, the percentage of referrals for PGD from internists increased significantly from 24% when patients asked about genetic testing fewer than 10 times, to 64% when patients asked about genetic testing more than 10 times. In another study, 68% of 373 gynaecological oncologists, obstetricians and gynae­cologists had incorrect or limited knowledge of PGD for hereditary breast and ovarian cancer and familial adenomatous polyposis. Although over 80% of the study participants stated that they would refer such patients to a PGD s­ pecialist, in reality this figure was only 29%.28 Internists and neurologists are familiar with the symptoms and signs of inherited neurological disorders—including those with variable late onset—and the dilemmas they pose for family members. However, neurologists or internists are not expected to have up-to-date knowledge of advances ADVANCE ONLINE PUBLICATION  |  1

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Oocyte retrieval


In vitro fertilization by ICSI

Fallopian tube


Ovary Glass needle Sperm

Transvaginal oocyte retrieval under ultrasound guidance

First polar body

Follicle Ultrasound probe


Embryo transfer

Test tube


Embryo biopsy for PGD Day 5 blastocyst Glass needle Trophectoderm cells

Inner cell mass (develops to embryo)


Normal embryo transferred into the uterus

Example PGD results

Embryo transfer Unaffected/normal chromosomes

Unaffected for the mutation and normal for 24 chromosomes

IVF–PGD over natural conception with prenatal testing. 29–31 Thus, conceiving a potentially healthy child by IVF–PGD is a preferred alternative for such patients. Except in the few countries where PGD is restricted, failure to inform patients of the option of PGD as a potential preventative measure could lead to litigation.32

Cryopreserved Affected

Abnormal chromosomes

Unaffected/normal chromosomes

Unaffected for the mutation, but trisomy chromosome 21 (Down syndrome)

Unaffected for the mutation and normal for 24 chromosomes


Figure 1 | In vitro fertilization with PGD. IVF is carried out to test for single gene disorders and chromosomal abnormalities (aneuploidy). a | Transvaginal oocyte retrieval under ultrasound guidance. b | In vitro fertilization of the oocyte by ICSI. c | A biopsy sample for PGD is taken from the trophectoderm of a blastocyst 5–6 days after fertilization. The inner cell mass develops into the embryo and the trophoectoderm develops into the placenta. d | An embryo, once found to be unaffected for the mutation and normal for 24 chromosomes by PGD, is transferred into the uterus. e | Example PGD results. Only unaffected embryos and embryos normal for all 24 chromosomes are used for implantation in the uterus. Affected or abnormal embryos can be discarded or donated to research. The remaining unaffected/normal embryos can be cryopreserved for future pregnancies. Abbreviations: ICSI, intracytoplasmic sperm injection; PGD, preimplantation genetic diagnosis.

in genetics, IVF and PGD. The aim of this Perspectives article is to better enable neurol­ogists to counsel patients with inherited neurological disorders and their family members on PGD.

Why choose PGD? Patients at risk of conceiving a child with an inherited fatal or debilitating disorder have several options. 14,24 They could conceive naturally and take the risk of having a sick

child, or have prenatal testing and face the dilemma to terminate the pregnancy or raise offspring with the disease. Alternatively, they could conceive using egg or sperm donations, adopt either an embryo or a child, or decide not to have children. The majority of at-risk couples prefer to have genetically related children; therefore, donated gametes or embryos are used only rarely.24 Moreover, studies of patient preferences revealed that about 80% of these couples would opt for


Safety Data obtained from IVF centres in the USA and Europe over the past decade have demonstrated that biopsy sampling for PGD, especially from the polar bodies 33,34 or trophectoderm on day 5–6 (the blastocyst stage) instead of from 3 day old embryos, has no measurable short-term impact on embryo development and does not significantly reduce pregnancy or delivery rates. 14,35–42 Single-embryo transfer after PGD can be offered to prevent multiple pregnancies, with similar delivery rates as for implantation after regular IVF or fertilization by intra­cyto­plasmic sperm injection (ICSI) cycles.36,43–47 These findings contrast with initial reports that suggested that biopsy samples taken for PGD might affect the rate of pregnancy with IVF.46 Prospective randomized trials showed that when a biopsy taken at the blastocyst stage was screened for aneuploidy via array comparative genome hybridization (aCGH) or quantitative realtime PCR (qPCR), embryo implantation rates improved significantly from 46% to 71% for women younger than 35 years old,48 and from 40% to 58% for women older than 35 years.45 Moreover, rates for ongoing pregnancy of over 20 weeks’ gestation improved from 42% to 69%. These rates are higher than those reported using biopsy of 3 day old embryos.48,49 Patients who opt for IVF for the purposes of PGD, with or without additional PGS for aneuploidy, can expect outcomes similar to or better than those in patients who receive IVF or ICSI for infertility only.14,40,42,45,49,50 Women younger than 35 years of age can expect excellent results with IVF–PGD treatment at experienced centres, with a delivery rate of 50‑70% per embryo transfer, depending on factors such as the reason for PGD, whether or not the individual has fertility problems, and whether or not PGS was carried out. In about 80–90% of IVF cycles, these women will have unaffected embryos available for transfer. Older women can expect lower pregnancy and delivery rates, similar to the age effect on pregnancy o ­ utcomes of IVF for infertility. Most importantly, children born after PGD

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PERSPECTIVES seem to have normal development without a significant increase in minor or major birth defects. 51–54 Although ran­d omized trials examining long-term outcomes have yet to be carried out, these findings are supported by two decades of experience at many centres worldwide.13,15,51–54 The possible errors and diagnostic failure of the modern genetics and PGD tests used today, such as microarray analysis of chromo­somes or genes, analysis of transcript expression by aCGH, single nucleotide polymorphism genotyping, qPCR, next-generation sequen­ cing and gene resequen­c ing, have been described by others.13,50,55–59 Similar to any genetic test, failure to inform patients about risks and error rates of PGD could lead to litigation, as can negligence in performing the procedure.32

Ethical considerations In the USA, because of reproductive rights and patients’ freedom to choose their care options, there are ethical guidelines on the use of PGD, but with no legal restrictions.19,20 PGD can be highly restricted to PGD testing on polar bodies only, as in Germany, or carefully regulated, as in the UK. The Human Fertilisation and Embryology Authority (HFEA), a public body sponsored and appointed by the Secretary of State for Health in the UK, serves as an independent regulator of treatments and research using eggs, sperm and embryos, including IVF and PGD. All parents wish for their children to be healthy. Parents have the option, and some argue that they have the obligation, to spare their future offspring from an inherited debilitating and fatal disorder and to provide them with a chance for the best life possible.31,60 The American Medical Association has stated that “the use of genetic technology to avoid the birth of a child with a gen­etic disorder is in accordance with the ethi­ cal principles associated with physicians’ thera­­peutic role.”61 Although prenatal testing with the potential termination of an affected embryo can be cost-effective (by reducing medical costs and loss of productivity of sick people with an incurable illness, as well as their caregivers) most couples (up to 80% in some surveys) would opt for PGD over natural conception with prenatal testing. PGD enables them to avoid the decision to abort an affected embryo or raise a sick child.30,62 When asked, only 32% of carriers of BRCA1 or BRCA2 mutations (which increase the likelihood of developing breast or ovarian cancer) had heard about PGD.

Table 1 | Neurological disorders for which PGD has been conducted* Inheritance pattern



Autosomal recessive

Aicardi–Goutieres syndrome Infantile diffuse degeneration of cerebral grey matter with hepatic cirrhosis Ataxia telangiectasia Canavan disease Citrullinaemia Cohen syndrome Fatal infantile cardioencephalomyopathy due to cytochrome C oxidase deficiency Friedreich ataxia Gangliosidosis Gaucher disease type 2 and type 3 Glycine encephalopathy Leigh syndrome Leukoencephalopathy with vanishing white matter Metachromatic leukodystrophy Neuronal ceroid lipofuscinosis 2 Phenylketonuria Sandhoff disease Smith–Lemli–Opitz syndrome Spinal muscular atrophy Succinic semialdehyde dehydrogenase deficiency Tay–Sachs disease Zellweger syndrome


Alzheimer disease Amyloidosis hereditary neuropathic disorder Charcot–Marie–Tooth disease axonal type 2E, demyelinating type 1A and type 1B Facioscapulohumeral muscular dystrophy 1A Familiar retinoblastoma Hypokalaemic periodic paralysis Huntington disease Myotonic dystrophy 1 Neurofibromatosis type 1 and type 2 Nonsyndromic holoprosencephaly Spinocerebellar ataxia type 1, type 2, type 6 and type 7 Tuberous sclerosis 1



Adrenoleukodystrophy Becker muscular dystrophy Charcot–Marie–Tooth disease Duchenne muscular dystrophy Emery–Dreifuss muscular dystrophy Fragile X syndrome Hydrocephalus Lesch–Nyhan syndrome Pelizaeus–Merzbacher-like disease Rett syndrome Spinal and bulbar muscular atrophy



Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes


Prion disorder

Gerstmann–Sträussler–Sheinker syndrome


Autosomal dominant



*Published sources6,10–17,78 or our own experience. Abbreviation: PGD, preimplantation genetic diagnosis.

However, 74% of at-risk individuals wished they had been given the option to learn about and discuss PGD, and 57% believed PGD to be an acceptable option.63 Over the years, and due to patient preferences, 62 the indications for PGD have expanded to include mitochondrial diseases and genetic predisposition for cancer with neurological involvement, as well as late-onset neurodegenerative disorders (Table 1), and HLA matching of a healthy


child to donate haematopoietic stem cells from the umbilical cord to potentially save a sick sibling.5,64–66 The American Society of Reproductive Medicine (ASRM) issued a Practice Committee Opinion on PGD in 2008, stating that “for couples known to be at risk for having children with a heritable and debilitating genetic disease, IVF with PGD represents a major scientific advance,” and “the birth of a healthy child validates the efficacy of PGD.”19 The authors ADVANCE ONLINE PUBLICATION  |  3

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PERSPECTIVES Box 1 | How to counsel patients about IVF with PGD ■■ A patient carrying a known genetic mutation or chromosomal abnormality can choose to use IVF–PGD to prevent transmission of the genetic abnormality to their offspring and future generations ■■ PGD is an early form of genetic testing and, when combined with IVF, enables gestation of only unaffected embryos. The clinical misdiagnosis rate is low (

Preimplantation genetic diagnosis for inherited neurological disorders.

Preimplantation genetic diagnosis (PGD) is an option for couples at risk of having offspring with an inherited debilitating or fatal neurological diso...
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