Gene 564 (2015) 119–124

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Review

Propionic acidemia in the Arab World Hatem Zayed Department of Health Sciences, Biomedical Program, Qatar University, Doha, Qatar

a r t i c l e

i n f o

Article history: Received 18 December 2014 Received in revised form 29 March 2015 Accepted 7 April 2015 Available online 9 April 2015 Keywords: Propionic acidemia PCCA PCCB Arabs Genotype–phenotype correlation Mutations

a b s t r a c t The autosomal recessive disease propionic acidemia (PA) is an inborn error of metabolism with highly variable clinical manifestations, caused by a deficiency of propionyl-CoA carboxylase (PCC) enzyme, due to mutations in either PCCA or PCCB genes, which encode the alpha and beta subunits of the PCC enzyme, respectively. The classical clinical presentation consists of poor feeding, vomiting, metabolic acidosis, hyperammonemia, lethargy, neurological problems, and developmental delay. PA seems to be a prevalent disease in the Arab World. Arab patients with PA seem to have the same classical clinical picture for PA with distinctive associated complications and other diseases. Most of the mutations found in Arab patients seem to be specific to the Arab population, and not observed in other ethnic groups. In this review, I will discuss in details the clinical and molecular profile of Arab patients with PA. © 2015 Elsevier B.V. All rights reserved.

Contents 1. 2.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Genotype–phenotype correlation in non-Arab PA patients belong to diverse ethnic groups 2.1. Strong genotype–phenotype correlation . . . . . . . . . . . . . . . . . . . . 2.2. Inconclusive genotype–phenotype correlation . . . . . . . . . . . . . . . . . 3. PA in Arabia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4. Clinical profile of Arab patients with PA . . . . . . . . . . . . . . . . . . . . . . . 5. Molecular studies in Arab patients with PA . . . . . . . . . . . . . . . . . . . . . . 6. Future directions and conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . Conflict of interest statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1. Introduction Propionic acidemia (PA; MIM# 232000 and 232050) is an autosomal recessive inherited inborn error of metabolism. It is caused by a deficiency of the mitochondrial enzyme propionyl-CoA carboxylase (PCC) enzyme (Hsia et al., 1971), which converts propionyl coenzyme A (propionyl-CoA) to methylmalonyl-coenzyme A (methylmalonyl-CoA), leading to impaired metabolism of branched-chain amino acids, such

Abbreviations: PA, propionic acidemia; IEMs, inborn errors of metabolism; PCC, propionyl-CoA carboxylase; PCCA, propionyl-CoA carboxylase, alpha subunit; PCCB, propionyl-CoA carboxylase, beta subunit. E-mail address: [email protected].

http://dx.doi.org/10.1016/j.gene.2015.04.019 0378-1119/© 2015 Elsevier B.V. All rights reserved.

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as isoleucine and valine, methionine, threonine, cholesterol side chains, odd numbered fatty acids, thymine and uracil. PCC enzyme is a dodecamer comprised of alpha and beta subunits; the alpha subunit is encoded by the PCCA gene (chromosome 13q32, MIM#232000; NCBI Reference Sequence: NG_008768.1). The beta subunit is encoded by the PCCB gene (chromosome 3q13.3–q22, MIM#232050; NCBI Reference Sequence: NG_008939.1) (Lamhonwah et al., 1986). Mutations in either the PCCA or PCCB gene cause PCC enzyme deficiency. To date, the Human Gene Mutation Database (http://www.hgmd. org) has reported 98 mutations in PCCA gene and 98 mutations in PCCB gene. According to the Exome variant service (EVS), 183 variants have been reported for the PCCA gene and 133 in the PCCB gene. The majority of these mutations were missense mutation (40%) (http://cbs.lf1.

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cuni.cz/pcc/pccmain.htm; Ugarte et al., 1999) followed by small insertions/deletions and splicing mutations. In the case of the PCCA gene, large genomic deletions were more frequent (Desviat et al., 2009). Patients with PA appear normal at birth; signs of disease might not appear in the first few days of life. Neonates with PA present with poor feeding, vomiting, hypotonia, lethargy, seizures, neurological problems, and developmental delay. Though PA is mostly an infantile disorder, as the patients advanced in age; disease progression is associated with complications affecting the cardiologic, neurologic, immunologic, hematologic, and gastrointestinal systems (Wolf et al., 1981; Henriquez et al., 1994; Lehnert et al., 1994; Ozand et al., 1994; Pena et al., 2012; Grunert et al., 2013; Rafique, 2013), rarely asymptomatic patients with PCC-deficient enzyme have been reported (Wolf et al., 1979). Propionic acidemia has been found to be accompanied by uncommon clinical signs such as intracranial bleeding (Ozand et al., 1994), seizures, and dehydration (Schreiber et al., 2012; Lehnert et al., 1994), and has also been found to be associated with different diseases such as Maple Syrup Urine (Van Calcar et al., 1992), mimicking diabetic ketoacidosis (Dweikat et al., 2011), premature ovarian failure (Lam et al., 2011), Noonan syndrome (Bouet et al., 2012), autism (Al-Owain et al., 2013), optic neuropathy (Arias et al., 2014), and chronic kidney disease (Vernon et al., 2014). Without a timely intervention to treat PA, the complications would likely lead to coma and death (Lehnert et al., 1994; Pena et al., 2012; Rafique, 2013; Vatanavicharn et al., 2014). The diagnosis of PA usually stems from clinical assessment and biochemical analyses: the most used definitive diagnostic test is gas chromatography/mass spectrometry (GC/MS) analysis of urine organic acids (Wojtowicz et al., 2010; Karam et al., 2013; Al-Owain et al., 2013). Plasma acylcarnitine analysis, which is used as part of newborn screening tests, is among the first diagnostic analysis performed (Rashed et al., 1995). Measuring the PCC enzyme activity and sequencing the PCCA and PCCB genes for potential pathogenic mutations are confirmatory tests, and used to uncover the molecular causes of the disease (Gravel et al., 1977; Saunders et al., 1979; Perez-Cerda et al., 2002) and to determine potential genotype– phenotype correlation. 2. Genotype–phenotype correlation in non-Arab PA patients belong to diverse ethnic groups

2.1. Strong genotype–phenotype correlation Strong relationship between the genotype and phenotype has been observed in many cases of PA. For example, two Middle Eastern patients, who were homozygous for the PCCB: c.1498+2TNC variant (Table 1), and have less than 0.1% of the normal PCCB transcript, presented with severe neonatal PA phenotype (Desviat et al., 2006). The PCCB: c.1301CNT (p.A434V) variant (Table 1) accounted for 50% of the PCCB mutant alleles in PA patients of Taiwanese origin, who have low enzyme activity and classic form of PA (Chiu et al., 2014). The PCCA: c.1118TNA (p.M373K) variant (Table 1) (Perez-Cerda et al., 2000; Clavero et al., 2002) is associated with early onset disease (Perez et al., 2010), and dramatically reduced in in vitro enzyme activity. On the other hand, two mutations, PCCA: c.223GNC (p.A75P) and PCCA: c.412GNA (p.A138T) (Table 1), were found in patients with mild phenotypes, consistent with the residual PCC enzyme activities of 26.7% and 9.4%, respectively (Desviat et al., 2004; Clavero et al., 2002). The PCCB: 1218del14ins12 mutation (p.G407fs) (Table 1) is the most common severe mutation among Caucasians, as it is found in 32% of mutant alleles (Lamhonwah et al., 1990; Tahara et al., 1993; Rodriguez-Pombo et al., 1998; Ugarte et al., 1999). This mutation is found to affect the protein function and is associated with an early onset and severe clinical phenotype (Perez et al., 2010). The PCC enzyme activity was not detectable in any cell lines that harbored this mutation (Perez-Cerda et al., 2000). Another representative example is the PCCB: c.1170insT mutation, which is prevalent in Hispanics; it affects the functionality of PCC protein and results in a premature stop codon and leads to the total absence of the beta subunit of the PCC enzyme (Table 1) (Lamhonwah et al., 1986; Rodriguez-Pombo et al., 1998; Ugarte et al., 1999), leading to a severe phenotype with an early onset of the disease (Perez-Cerda et al., 2000). The PCCB: c.1283CNT (p.T428I) mutation is common among Japanese and Koreans (Table 1) (Ohura et al., 1993; Ugarte et al., 1999; Kim et al., 2002; Yang et al., 2004) and inactivates PCC enzyme (Kelson et al., 1996), which is consistent with a severe form of PA and neonatal disease presentation (Kim et al., 2002). All of the severe clinical phenotype of these mutations is in agreement with the classical clinical findings of the PA, including, hyperammonemia, metabolic acidosis, and poor feeding and vomiting. 2.2. Inconclusive genotype–phenotype correlation

The ability to measure the PCC enzyme activity and molecularly test for mutations for both PCCA and PCCB genes, made it conducive to draw a potential relationship between the genotype and the clinical features of patients with PA. The effect of mutations on the PCC enzyme activity, in silico prediction, family history, age of onset,and clinical features, were compiled to reach a conclusion on the clarity of the relationship between the genotype and phenotype of patients with PA.

Although some studies showed a direct correlation between the genotype and the clinical phenotype, it is not always possible to draw conclusions about the phenotype from the genotype. For example, the PCCB: c.1228CNT (p.R410W) mutation (Table 1), which is frequently associated with Japanese patients with PA (Ohura et al., 1993; Tahara et al., 1993), exhibited 12% residual enzyme activity (Perez-Cerda

Table 1 genotype–phenotype correlation for PA patients in different ethnic groups. Origin

Gene

N change

AA change

PCC_A

PP

CP

Reference

Latin USA Spain USA, Latin Spain Japan, Korea Japan Latin Taiwan Iran/Pakistan

PCCA PCCA PCCA PCCB PCCB PCCB PCCB PCCB PCCB PCCB

c.1118TNA c.223GNC c.412GNA 1218del14ins12 1170insT c.1283CNT c.1228CNT c.502GNA c.1301CNT 1498+2TNCa

p.M373K p.A75P p.A138T p.G407fs N/A p.T428I p.R410W p.E168K p.A434V p. A468fs

2% 26.7% 9.4%, Null 1.2% Null 12% 1.7% 3.9%

PD PD PD N/A N/A PD PD PD PD N/A

Severe Mild Mild Severe Severe Severe Severe Mild–severe Severe Severe

Clavero et al., 2002; Perez et al., 2010 Desviat et al., 2004; Clavero et al., 2002. Desviat et al., 2004; Clavero et al., 2002. Desviat et al., 2004 Perez-Cerda et al., 2000 Desviat et al., 2004 Perez-Cerda et al., 2003; Ohura et al., 1993 Rodriguez-Pombo et al., 1998; Perez-Cerda et al., 2000 Chiu et al., 2014 Desviat et al., 2006

b

Abbreviations: N: nucleotide, PP: polyphen2 prediction, PCC_A: PCC mutant enzyme activity related to normal, PD: probably damaging. Note: the value of a polyphen2 is very limited, when expression data are available. a This variant led to exon skipping with a significant reduction of the splicing score from 84.7 to 66.9, measured by using the gene bank database (Shapiro and Senapathy, 1987), indicating affected function phenotype. b This variant led to skipping of exon 14 of the PCCB gene, leading to a frameshift mutation (p.A468fs). The amount of the normal spliced transcripts in the patients' cells, were less than 0.1% of the normal transcript of the normal control.

H. Zayed / Gene 564 (2015) 119–124

et al., 2003), and kinetic analysis (Jiang et al., 2005) indicated that this variant retained 50% of the catalytic activity of the PCC enzyme. While these in vitro findings are consistent with a mild phenotype, this variant is often found in patients who are severely affected. Polyphen2 prediction for this mutation is a “probably damaging” phenotype. Another challenging example for the genotype–phenotype correlation is the PCCB: c.502GNA (p.E168K) variant (Table 1), which results in a broad spectrum of phenotypic manifestations in both the homozygous and compound heterozygous forms, ranging from mild signs and symptoms consistent with late manifestation, to a severe phenotype with an early presentation (Rodriguez-Pombo et al., 1998; Perez-Cerda et al., 2000; Desviat et al., 2004), which is probably due to the variability in the enzyme activity (Jiang et al., 2005), though the mutation clinical significance is categorized as pathogenic/likely pathogenic (ClinVar), and predicted to be damaging to the PCC enzyme activity using in silico predictions. It is indeed challenging to draw a clear-cut picture for the genotype– phenotype correlation for patients with PA (Pena et al., 2012). This might be due to several reasons: most patients with PA are compound heterozygous (Perez-Cerda et al., 2000; Clavero et al., 2002; Yang et al., 2004; Jiang et al., 2005), variable enzyme activities due to the variability of the in vitro transfection assays used to measure PCC enzyme activity of the mutant alleles (Richard et al., 1999; Clavero et al., 2002; Yang et al., 2004), two genes controlling the assembly of the PCC holoenzyme and the mutations in either PCCA or PCCB or both, sometimes making it impossible to draw a precise correlation between these mutations and their clinical presentations, most of the patients diagnosed with PA have not yet been molecularly characterized (Lehnert et al., 1994; Rafique, 2013, 2014), and finally it seems that there are population-specific mutations, and it is not possible to predict their effect on other ethnic groups with different genetic makeup. 3. PA in Arabia PA seems to be a prevalent disease in the Arab World and considered to be a health threat in Arab population due to the high prevalence of intra-familiar marriage. It has been reported in many Arab countries, including Saudi Arabia (Rashed et al., 1994; Al Essa et al., 1998; Rashed, 2001; Al-Odaib et al., 2003; Kaya et al., 2008), Bahrain (Al-Arrayed, 2006), Qatar (Al-Rikabi and Al-Homsi, 2004), UAE and Oman (Joshi et al., 2002; Joshi and Venugopalan, 2007; Al Riyami et al., 2012; Al-Shamsi et al., 2014), Tunisia (Hadj-Taieb et al., 2012), Jordan (Al-Qa'qa' et al., 2012), Palestine (Dweikat et al., 2011), Egypt (Hassan et al., 2009; Ghoraba et al., 2014; Selim et al., 2014), Lebanon (Karam et al., 2013), and among patients with a Syrian, Iraqi, and Lebanese origin (Kraus et al., 2012). The global incidence of PA occurs in 1:50,000 to 1:100,000 (NuCarrillo-Carrasco and Venditti, propionic acidemia (GeneReviews, http://www.ncbi.nlm.nih.gov/books/NBK92946)). In the US, it is estimated to be 1:35,000 live births. However, in other ethnic groups the incidence is much higher: among the Inuit population of Greenland, 1:1000 (Ravn et al., 2000), in Saudi Arabia, 1:27,264 in live births (Moammar et al., 2010), and it is much higher in rate specifically in four specific Saudi tribes, ranging from 1:2000 to 1:5000 (Ozand et al., 1994; Rashed et al., 1994), where first cousin marriage is extremely prevalent (Chapman and Summar, 2012). It is a challenging task to determine the overall prevalence of PA in the Arab World due to the under-reported cases of the disease, and the undeveloped infrastructure of universal genetic testing programs in the 22 Arab states. Given the high frequency of consanguineous marriage in the Arab World (Tadmouri et al., 2009), which is responsible for the high frequency of genetic diseases in Arabia (Al-Gazali et al., 2006), the PA prevalence in Arabia is expected to be significantly higher. The global Arab prevalence of PA is not available, due to the vast variation of the degree of the development and implementations of the genetic screening programs in Arabia as well as the lack of universality in the application of these

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programs in countries which already have active screening programs. Al-Shamsi et al. (2014) performed a study to estimate the birth prevalence and mutation spectrum of inborn errors of metabolism (IEMs) among Emiratis between 1995 and 2012. A total of 37 distinct IEM patients were found in Emirati neonates, providing an estimated IEM birth prevalence of 75.24 per 100,000 live births. PA was found to be one of the most prevalent IEMs identified in this study, with a birth prevalence of 2.2–4.9 per 100,000. Al-Arrayed (2006) indicated that the incidence of PA occurs in Bahrain of 1/10,000 births. 4. Clinical profile of Arab patients with PA There have been several studies which have reported on the clinical characteristics of Arab patients with PA. However, it is important to note that several methods are used to establish a diagnosis of PA in Arabia. Most of the studies have relied on the detection of high level of propionylcarnitine in the blood using tandem mass spectrometry (MS/ MS) and in urine using high performance liquid chromatography (HPLC) (Joshi and Venugopalan, 2007; Hassan et al., 2009, Al Riyami et al., 2012; Al-Owain et al., 2013; Karam et al., 2013; Ghoraba et al., 2014); detection of propionate metabolites excreted in the urine using GC/MS; PCC enzyme activities; and PCCA and PCCB gene sequencing analysis (Al-Rikabi and Al-Homsi, 2004; Desviat et al., 2004; Ali et al., 2011; Shuaib et al., 2012; Kraus et al., 2012; Al-Owain et al., 2013; Al-Shamsi et al., 2014). Most Arab patients with PA showed an early age of onset (Joshi et al., 2002; Al Riyami et al., 2012; Rafique, 2013, Al-Shamsi et al., 2014; Rafique, 2014; Selim et al., 2014); most of which appeared in the neonatal period accompanied with severe symptoms; most commonly ketoacidosis and hyperammonemia. This was in agreement with other ethnic groups, such as Asians (Yang et al., 2004; Vatanavicharn et al., 2014), South Americans, Europeans, and North Americans (Kim et al., 2002; Perez et al., 2003; Perez et al., 2010; Kraus et al., 2012; Grunert et al., 2013), though a study screened for patients with PA from Central Spain found equal distribution of the early and late onset forms of the disease in Spanish patients (Perez-Cerda et al., 2003). Late onset disease among Arab patients has also been observed to a much lower degree (Rafique, 2013; Rafique, 2014; Selim et al., 2014), characterized with a less severe profile, and typically, symptoms appear after the third month of life and patients have longer survival rates. Interestingly, the Arab picture of patients with PA draws more males affected with PA than females (Joshi and Venugopalan, 2007; Al Riyami et al., 2012; Rafique, 2013; Rafique, 2014). This has been observed in European patients with PA (Grunert et al., 2013). Although the overall clinical picture of the Arab patients with PA is not distinct from the classical clinical form of PA, typically presenting with poor feeding, vomiting, hypotonia, lethargy, metabolic acidosis, and hyperammonemia (Rafique, 2013; Rafique, 2014; Selim et al., 2014), it seems to be more associated with less common or atypical findings such as hypoglycemia (Joshi and Venugopalan, 2007; Rafique, 2013); severe coma (Rafique, 2013); acute neonatal encephalopathy (Joshi and Venugopalan, 2007; Karam et al., 2013); erythematous and scalded skin; primary hypothyroidism (Al-Rikabi and Al-Homsi, 2004); autism (Al-Owain et al., 2013); and visual hallucinations were reported on a 13-years old Saudi patient (Shuaib et al., 2012) born to consanguineous parents, who was diagnosed with PA at the first week of his life. The patient has a negative family history for psychiatric illness, mild metabolic acidosis and hyperammonemia. The child presented at the age of ten with visual hallucinations, significant diffuse atrophic changes of cerebral hemisphere, and basal ganglia. Interestingly, in the same study, another patient from a Pakistani decent was diagnosed with PA associated with comparable symptoms related to visual hallucination at six years of age. There was also the case of a seven year old female child from Qatar (Al-Rikabi and Al-Homsi, 2004), who presented with erythematous and scalded skin lesion on her limbs and trunk. She had been previously

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diagnosed with PA due to complete loss of PCC enzyme activity, also associated with primary hypothyroidism. She suffered from erythematous and scalded skin lesions. Treatment with zinc supplements resulted in improvement of the skin lesions. However, the patient died due to staphylococcal septicemia. The authors suggested that the serum zinc deficiency and PA is a single disease with variable presentation. To the contrary, other studies found normal levels of zinc in the serum of patients with PA (Tabanlioglu et al., 2009), and the zinc deficiency is probably connected to unrelated cutaneous manifestations (Sehgal and Jain, 2000). Infection complications of unusual microorganisms have been associated with 80% of Saudi patients with PA in a study done by Al Essa et al. (1998). The infections were found to be persistent despite appropriate diet therapy and aggressive treatment. Certain tribes accounted for almost 80% of these cases, and about 50% of the patients died during the neonatal period. The persistence of infections in the majority of PA patients may be related to an underlying immune deficiency. Indeed when Al Essa et al. (1998) investigated three patients with PA for the immune parameters between acute metabolic attacks, a severe decrease in CD4 cells was found, with reversal of CD4/CD8 ratio, and the gamma-globulin was deficient, in addition, other immunological abnormalities also being observed. This finding is consistent with the finding of Henriquez et al. (1994), indicating that Arab patients with PA are prone to serious infections, probably due to immunodeficiency. In 2004, Lucke et al. (2004) reported a 4 1/2-year-old German girl who was compound heterozygous for two missense mutations in PCCA gene; she became comatose following a simple infection. The Al Essa et al. (1998) study concludes that infection is a frequent problem among Saudi patients with PA. Although the clinical profile of Arab patients is considered to be heterogeneous, as is the case in the classical form of PA in other ethnic groups, several clinical findings are considered to be characteristic and distinct among Arab patients. For example, the association of autism and PA in the same Arab patient (Al-Owain et al., 2013; Ghaziuddin and Al-Owain, 2013) which was not found in any other ethnicity. Hypoglycemia is found to be more frequent among Omanis (Joshi and Venugopalan, 2007) and Saudi patients (Rafique, 2013) than in Europeans (Lehnert et al., 1994), but not noticeable in PA patients from Egypt (Selim et al., 2014). Frequent infections with uncommon infectious agents in Arab PA patients; and subsequently, combined with underling immunodeficiency (Al Essa et al., 1998; Henriquez et al., 1994), compared to a single case in a Caucasian patient from Germany (Lucke et al., 2004). Though the number used in these studies is not large enough to draw a conclusive picture of the Arab PA patients regarding the susceptibility to infection with unusual microbes, but these studies suggest that there might be underlying immune defects associated with Arab patients, in particular Saudi patients, compared to other ethnic groups. 5. Molecular studies in Arab patients with PA Many patients in Arabia have been reported to have PA, but unfortunately most of the patients have not been sequenced (Rashed et al., 1994; Al Essa et al., 1998; Rashed, 2001; Al-Odaib et al., 2003; Al-Rikabi and Al-Homsi, 2004; Joshi and Venugopalan, 2007; Hassan et al., 2009; Dweikat et al., 2011; Al Riyami et al., 2012; Al-Qa'qa' et al., 2012; Hadj-Taieb et al., 2012; Karam et al., 2013; Rafique, 2013; Rafique, 2014; Ghoraba et al., 2014). Few studies have identified several mutations circulating among Arab patients: one molecular analysis study by Kaya et al. (2008) investigated the genomic DNA derived from two Saudi siblings diagnosed with PA. The assays used for molecular analysis were PCR, long-PCR, and array comparative genomic hybridization (aCGH). The results showed an approximately 73 kb deletion extending from intron 16 to intron 19 and an 18 bp insertion at the distal end of the deletion in PCCA gene. The deletion is considered to be novel and the largest reported so far for the PCCA gene. The

deletion in a homozygous form is responsible for a mild-severe phenotype for PA, and has not been reported in other ethnicity so far. Another study reported on a 13-year old Saudi boy diagnosed with PA in the first week of his life, who had visual hallucinations (Shuaib et al., 2012). He was found to harbor a homozygous missense variant PCCA: 350G N A (p.G117D) (Table 2). The same variant was observed in a homozygous form in another Saudi female patient diagnosed with PA and autism (Al-Owain et al., 2013). This variant was not noted in other ethnic groups. In a study aimed to estimate the birth prevalence of IEMs among Emiratis neonates in the UAE (Al-Shamsi et al., 2014), five neonates were diagnosed with PA: two patients harbored a novel 4-bp deletion frame-shift variant PCCA: c.1598_1601delTTGT (p.F533Wfs*5) (Table 2), leading to the truncation of the expressed protein. The other three patients had two different variants: a missense variant PCCB: c.1142GNA (p.C381Y) and a duplication variant PCCB: c.990dupT (p.E331*). The c.990dupT was found in two separate tribes originally from Oman. This variant was previously identified in Latin patients (Perez et al., 2003; Desviat et al., 2004; Perez et al., 2010); Spanish patients (Perez-Cerda et al., 2003), and in a homozygous Turkish patient (Kraus et al., 2012). A compound heterozygous form of this variant (p.R410W/p.E331*) retains a residual activity of the normal PCC enzyme in fibroblasts derived from a Spanish patient (Perez-Cerda et al., 2003), which deteriorate the functionality of PCC enzyme activity (Table 2) (Kraus et al., 2012). The residual activity is related to p.R410W variant, which retains substantial PCC activity in in vitro assay (Perez-Cerda et al., 2003). The p.E331* variant is clearly affecting the protein function due to the premature stop codon and the truncation of the PCCB subunit protein, leaving the terminal 208 amino acids. Kraus et al. (2012) used DNA extracted from lymphoblast cells of 54 patients with PA residing in Germany, Austria, and Switzerland. Two Arab patients were diagnosed with PA through newborn screening: the first was a Syrian male diagnosed at 7.1 years of age, with no reported consanguinity. He manifested tachypnea on day 1 of life. Molecular analysis revealed that the patient had a homozygous missense variant PCCB: c.1313CNT (p.A438V), which abolished the PCC enzyme activity (Table 2). The second patient is a male of a Lebanese decent, with reported consanguinity. He was diagnosed at 1.3 years of age and presented with feeding refusal, failure to thrive, vomiting, hypotonia, and diarrhea at the age of onset (day 3). He found to be homozygous for a single base deletion in exon 12; PCCA: c.923delT (p.L308fs), and heterozygous for a missense variant PCCB:c.1352CNT (p.T451I). The in vitro expression of p.T451I variant yielded 13.4% of normal enzyme activity (Desviat et al., 2004; Kraus et al., 2012). The PCCA: p.L308fs variant was reported in two Turkish patients (Kraus et al., 2012). In the same study (Kraus et al., 2012) two Iraqi siblings were reported to have the same homozygous splice variant PCCB: c.183+2TNC (p.Arg61fs) (Table 2), which was previously reported in a Kurdish patient with PA (Desviat et al., 2006). Desviat et al. (2009) have reported a deletion variant PCCA: c.1066-?_1284+?del (p.V356_G428del73) in a patient from Lebanon, which led to the deletion of exons 13 and 14. Two other Arab patients with PA were found to harbor a homozygous deletion in exon 23 of PCCA gene (c.2041-2924del3889) (Table 2) (Perez et al., 2003): one patient was diagnosed in the USA and the second patient diagnosed in Belgium (Table 2). The two variants were found in combination with a p.V551F SNP variant in the PCCA gene. A third Arab patient was presented with an early onset of the disease, and was homozygous for this PCCB: c.543+1GNA variant (Perez et al., 2003) (Table 2). The Arab World is comprised of 22 Arab-speaking countries, an area extended from the Atlantic Ocean in the west to the Arabian Sea in the east. The Arab population is approaching 0.5 billion, and this region has been extensively exposed to many successive invaders from Turkey, Romans, and Europe, as well as traders and immigrants contribute to mixing the ethnic demographic of the population, which will explain the gene flow exchange among the Arabs and these different ethnicities. Though the Arab PA patients have unique molecular signature, there are

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Table 2 Summary of the mutations found in Arab patients diagnosed with PA. Origin

Gene

N change

AA change

PCC_A

PP

CP

P no

Reference

UAE Saudi Arabia Lebanon Arab (Belgium) Arab (USA) Lebanon Syria UAE/Oman UAE/Oman Lebanon Iraq Arab (USA)

PCCA PCCA PCCA PCCA PCCA PCCA PCCB PCCB PCCB PCCB PCCB PCCB

c.1598_1601delTTGT c.350GNA c.923delT c.2041-2924del3889 c.2041-2924del3889 c.1066-?_1284+?del c.1313CNT c.1142GNA c.990dupT c.1352CNT c.183+2TNC c.543+1GNA

p.F533Wfs*5 p.G117D p.L308fs N/A N/A p.V356_G428del73 p.A438V p.C381Y p.E331* p.T451I p.Arg61fs p.I144-L181del37

– – – – – – 1.5% – – 13.4% – –

N/A PD N/A N/A N/A N/A PD PD N/A B N/A N/A

– Mild Severe Severe – – – – severe – Severe –

2 2 1 1 1 1 1 3 4 1 2 1

Al-Shamsi et al. (2014) (Shuaib et al., 2012; Al-Owain et al., 2013) Kraus et al., 2012 Perez et al., 2003 Perez et al., 2003 Desviat et al., 2009 Kraus et al., 2012 Al-Shamsi et al. (2014) Ali et al., 2011; Al-Shamsi et al. (2014) Kraus et al., 2012; Desviat et al., 2009 Kraus et al., 2012 Perez et al., 2003

Abbreviations: PCC: propionyl-CoA carboxylase, – : nor reported, CP: clinical phenotype, N/A: not applicable, P no: patients' no, N: nucleotide, PP: polyphen2 prediction, PCC_A: PCC mutant Activity related to normal, PD: probably damaging, B: Benign. Note: the value of a polyphen2 is limited, when expression data are available.

some variants which are shared with different ethnic groups such as the Latin and Spanish and Turkish (c.990dupT); Turkish (p.L308fs); and Kurdish (p.Arg61fs). The recurrent observation of these mutations among different ethnic groups clearly reflects a history of admixture and mutant gene migration among these populations. Missense mutations were the most common mutations found among Arab patients followed by deletion mutations (Table 2), which is in agreement with other ethnic groups (Ugarte et al., 1999; Desviat et al., 2009). It is challenging to determine the founder mutations or predominant disease-causing alleles in Arab patients due to the few molecular characterizations of Arab patients. Most of Arab PA patients were not sequenced and the majority of sequenced patients were not clinically investigated. Therefore, it is not possible to draw a clear relationship between the genotype and clinical phenotype of the Arab patients with PA, at least for the near future. 6. Future directions and conclusion The ability to analyze the expression and sequence of PCCA and PCCB genes in patients with PA, has allowed us to better understand the potential genotype–phenotype correlations. This has been observed in patients from different ethnic background, originating from Europe, USA, Japan, Korea, Iran, Pakistan (Clavero et al., 2002; Desviat et al., 2004), Taiwan (Chiu et al., 2014) and Latin America (Desviat et al., 2004; Perez et al., 2010). However the genetic heterogeneity presents a challenge for a straightforward conclusion for this correlation, and in order to reach a deep understanding for such relationship, more patients need to be investigated across different ethnic groups, and other shared mutations need to be characterized. Molecular analysis studies of Arab patients are needed to further identify the disease causing mutations of PA in Arabia. These studies should aim to comprehensively analyze the entire sequences of both the PCCA and PCCB genes, including the introns; exons; and the regulatory sequences, and check for possible modifier genes and potential polymorphism, followed by methodical clinical and biochemical investigation of these patients to precisely pinpoint the genotype–phenotype correlation. It is important to dedicate more studies to emphasize the understanding of the mutation type, location, mutation effect on PCC gene expression, clinical severity, and diagnosis. Establishing an Arab registry to collect and establish an inventory of all this data will provide a wealth of patients' data about the disease, which will be communicated to Arab scientists, and medical and public health professionals across the 22 Arab countries. This is expected to provide protocols and guidance for application of appropriate preventative measures such as prenatal diagnosis, newborn screening and appropriate diet for the neonates diagnosed with PA. This will also educate physicians about the clinical nature of the disease and the associated complications for better prognosis and diagnosis of the disease, in addition to increasing

awareness among the Arab public for the potential risk of consanguineous marriage, and the importance of integrating the prenatal screening as an essential part of the health-care system in Arabia. The clinical picture of Arab patients with PA seems not to be distinct from the classical picture of patients in other ethnicities, but there seems to be distinctive clinical complications associated with Arab patients that has not existed or is not as prevalent in other ethnic groups. Though few molecular analyses have been performed for Arab patients, it seems there is a molecular distinctive picture for Arab patients, as most of the mutations found in Arab patients were novel and have not been noted in other ethnicities. Therefore, there is a definite need for comprehensive molecular characterization for Arab patients to improve the prognosis of the disease and to better understand the genotype– phenotype correlation of PA. To this end, molecular studies of both newly diagnosed and wellcharacterized Arab patients with PA will improve our understanding of the molecular pathology of PA, contribute to the development of accurate and precise molecular diagnostics for the disease, and promote better understanding of the genotype–phenotype correlation of PA. Early prenatal diagnosis will be an important preventative measure to improve outcome in certain patients suffering from PA in Arabia. Conflict of interest statement Hatem Zayed declares that he has no conflict of interest. References Al Essa, M., Rahbeeni, Z., Jumaah, S., et al., 1998. PT infectious complications of propionic acidemia in Saudi Arabia. Clin. Genet. 1998 (54), 90–94. Al Riyami, S., Al Maney, M., Joshi, S.N., Bayoumi, R., 2012. Detection of inborn errors of metabolism using tandem mass spectrometry among high-risk Omani patients. Oman Med. J. 27, 482–485. Al-Arrayed, S.S., 2006. Genetic Disorders in the Arab World. pp. 74–91 (Chapter 5). Al-Gazali, L., Hamamy, H., Al-Arrayad, S., 2006. Genetic disorders in the Arab world. BMJ. 7573, 831–834. Ali, B.R., Hertecant, J.L., Al-Jasmi, F.A., et al., 2011. New and known mutations associated with inborn errors of metabolism in a heterogeneous Middle Eastern population. Saudi Med. J. 32, 353–359. Al-Odaib, A.N., Abu-Amero, K.K., Ozand, P.T., Al-Hellani, A.M., 2003. A new era for preventive genetic programs in the Arabian Peninsula. Saudi Med. J. 24, 1168–1175. Al-Owain, M., Kaya, N., Al-Shamrani, H., et al., 2013. Autism spectrum disorder in a child with propionic acidemia. JIMD Rep. 7, 63–66. Al-Qa'qa', K., Amayreh, W., Al-Hawamdeh, A., 2012. Spectrum of inborn errors of metabolism in Jordan: five years of experience at King Hussein Medical Center. JRMS 4, 37–41. Al-Rikabi, A.C., Al-Homsi, H.I., 2004. Propionic acidemia and zinc deficiency presenting as necrolytic migratory erythema. Saudi Med. J. 2004 (25), 660–662. Al-Shamsi, A., Hertecant, J.L., Al-Hamad, S., Souid, A.K., Al-Jasmi, F., 2014. Mutation spectrum and birth prevalence of inborn errors of metabolism among Emiratis: a study from Tawam Hospital Metabolic Center, United Arab Emirates. Sultan Qaboos Univ. Med. J. 14, 42–49. Arias, C., Raimann, E., Peredo, P., Cabello, J.F., et al., 2014. Propionic acidemia and optic neuropathy: a report of two cases. JIMD Rep. 12, 1–4.

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