Adel Shalata

The deoxyguanosine kinase gene is mutated in individuals with depleted hepatocerebral mitochondrial DNA.

Mitochondrial DNA (mtDNA)–depletion syndromes (MDS; OMIM 251880) are phenotypically heterogeneous, autosomal-recessive disorders characterized by tissue-specific reduction in mtDNA copy number. Affected individuals with the hepatocerebral form of MDS have early progressive liver failure and neurological abnormalities, hypoglycemia and increased lactate in body fluids. Affected tissues show both decreased activity of the mtDNA-encoded respiratory chain complexes (I, III, IV, V) and mtDNA depletion. We used homozygosity mapping in three kindreds of Druze origin to map the gene causing hepatocerebral MDS to a region of 6.1 cM on chromosome 2p13, between markers D2S291 and D2S2116. This interval encompasses the gene (DGUOK) encoding the mitochondrial deoxyguanosine kinase (dGK). We identified a single-nucleotide deletion (204delA) within the coding region of DGUOK that segregates with the disease in the three kindreds studied. Western-blot analysis did not detect dGK protein in the liver of affected individuals. The main supply of deoxyribonucleotides (dNTPs) for mtDNA synthesis comes from the salvage pathway initiated by dGK and thymidine kinase-2 (TK2). The association of mtDNA depletion with mutated DGUOK suggests that the salvage-pathway enzymes are involved in the maintenance of balanced mitochondrial dNTP pools.

Mutations in SLC19A2 cause thiamine-responsive megaloblastic anaemia associated with diabetes mellitus and deafness.

Thiamine-responsive megaloblastic anaemia (TRMA), also known as Rogers syndrome, is an early onset, autosomal recessive disorder defined by the occurrence of megaloblastic anaemia, diabetes mellitus and sensorineural deafness, responding in varying degrees to thiamine treatment (MIM 249270). We have previously narrowed the TRMA locus from a 16-cM to a 4-cM interval on chromosomal region 1q23.3 (Refs 3, 4) and this region has been further refined to a 1.4-cM interval. Previous studies have suggested that deficiency in a high-affinity thiamine transporter may cause this disorder. Here we identify the TRMA gene by positional cloning. We assembled a P1-derived artificial chromosome (PAC) contig spanning the TRMA candidate region. This clarified the order of genetic markers across the TRMA locus, provided 9 new polymorphic markers and narrowed the locus to an approximately 400-kb region. Mutations in a new gene, SLC19A2, encoding a putative transmembrane protein homologous to the reduced folate carrier proteins, were found in all affected individuals in six TRMA families, suggesting that a defective thiamine transporter protein (THTR-1) may underlie the TRMA syndrome.

Hypotrichosis with juvenile macular dystrophy is caused by a mutation in CDH3, encoding P-cadherin

Congenital hypotrichosis associated with juvenile macular dystrophy (HJMD; MIM601553) is an autosomal recessive disorder of unknown etiology, characterized by hair loss heralding progressive macular degeneration and early blindness. We used homozygosity mapping in four consanguineous families to localize the gene defective in HJMD to 16q22.1. This region contains CDH3, encoding P-cadherin, which is expressed in the retinal pigment epithelium and hair follicles. Mutation analysis shows in all families a common homozygous deletion in exon 8 of CDH3. These results establish the molecular etiology of HJMD and implicate for the first time a cadherin molecule in the pathogenesis of a human hair and retinal disorder.

Intra-Familial Clinical Heterogeneity: Absence of Genotype-Phenotype Correlation in Primary Hyperoxaluria Type 1 in Israel

Background/Aims: Primary hyperoxaluria type 1 (PH1) is caused by the deficiency of the liver enzyme alanine:glyoxylate aminotransferase which results in increased synthesis and excretion of oxalate. The clinical manifestations of PH1 are heterogeneous with respect to the age of onset and rate of progression. The aim of this study was to investigate possible relationships between a given genotype, the biochemical profile and the clinical phenotype. Methods: We conducted a study of 56 patients from 22 families with PH1 from Israel. The clinical and biochemical data were compiled and the genotype was determined for each family. Results: The prevalent phenotype was of early onset with progression to end-stage renal disease during the first decade of life. Fifteen PH1-causing mutations were detected in 21 families: 10 were first described in this patient population. Marked intra-familial clinical heterogeneity was noted, meaning that there was no correlation between a given genotype and the phenotype. Conclusions: The clinical course of patients with PH1 is not dictated primarily by its genotype. Other genetic and/or environmental factors play a role in determining the ultimate phenotype.

Myotonia congenita in a large consanguineous Arab family: insight into the clinical spectrum of carriers and double heterozygotes of a novel mutation in the chloride channel CLCN1 gene.

The aims of this study were to (1) characterize the clinical phenotype, (2) define the causative mutation, and (3) correlate the clinical phenotype with genotype in a large consanguineous Arab family with myotonia congenita. Twenty‐four family members from three generations were interviewed and examined. Genomic DNA was extracted from peripheral blood samples for sequencing the exons of the CLCN1 gene. Twelve individuals with myotonia congenita transmitted the condition in an autosomal dominant manner with incomplete penetrance. A novel missense mutation [568GG>TC (G190S)] was found in a dose‐dependent clinical phenotype. Although heterozygous individuals were asymptomatic or mildly affected, the homozygous individuals were severely affected. The mutation is a glycine‐to‐serine residue substitution in a well‐conserved motif in helix D of the CLC‐1 chloride channel in the skeletal muscle plasmalemma. A novel mutation, 568GG>TC (G190S) in the CLCN1 gene, is responsible for autosomal dominant myotonia congenita with a variable phenotypic spectrum. Muscle Nerve, 2009

Prenatal diagnosis and carrier detection for molybdenum cofactor deficiency type A in Northern Israel using polymorphic DNA markers

Molybdenum cofactor deficiency (MoCoD) is an autosomal recessive, fatal neurological disorder, characterized by the combined deficiency of sulphite oxidase, xanthine dehydrogenase and aldehyde oxidase. We have recently reported an excessive occurrence of this fatal disorder among segments of the Arab population in Northern Israel suggesting that the true incidence of MoCoD is probably underestimated in this highly inbred population. This lethal disease can be diagnosed prenatally by assay of sulphite oxidase activity in chorionic villus samples in pregnancies of couples who have had previously affected children (obligatory carriers). However, to date, there is no biochemical assay for carrier detection among the population at risk. Recently we demonstrated the linkage of a MoCoD gene to an 8‐cM region on chromosome 6p21.3 in two consanguineous Israeli–Arab unrelated kindreds. The description of the MOCS1 gene that maps to the same region and which carries multiple mutations in MoCoD type A followed this finding. We describe here one additional kindred of Arab–Israeli origin, which is also linked to the MOCS1 locus, and demonstrate the feasibility of prenatal diagnosis and carrier detection using microsatellite markers in selected families when mutations are unknown. A complete correlation between the biochemical and DNA assays was found in a total of six samples (five chorionic villus and one amniocyte culture sample) obtained from the three MoCoD families. Copyright

Sequence variation in PPP1R13L results in a novel form of cardio‐cutaneous syndrome

Dilated cardiomyopathy (DCM) is a life‐threatening disorder whose genetic basis is heterogeneous and mostly unknown. Five Arab Christian infants, aged 4–30 months from four families, were diagnosed with DCM associated with mild skin, teeth, and hair abnormalities. All passed away before age 3. A homozygous sequence variation creating a premature stop codon at PPP1R13L encoding the iASPP protein was identified in three infants and in the mother of the other two. Patients’ fibroblasts and PPP1R13L‐knocked down human fibroblasts presented higher expression levels of pro‐inflammatory cytokine genes in response to lipopolysaccharide, as well as Ppp1r13l‐knocked down murine cardiomyocytes and hearts of Ppp1r13l‐deficient mice. The hypersensitivity to lipopolysaccharide was NF‐κB‐dependent, and its inducible binding activity to promoters of pro‐inflammatory cytokine genes was elevated in patients’ fibroblasts. RNA sequencing of Ppp1r13l‐knocked down murine cardiomyocytes and of hearts derived from different stages of DCM development in Ppp1r13l‐deficient mice revealed the crucial role of iASPP in dampening cardiac inflammatory response. Our results determined PPP1R13L as the gene underlying a novel autosomal‐recessive cardio‐cutaneous syndrome in humans and strongly suggest that the fatal DCM during infancy is a consequence of failure to regulate transcriptional pathways necessary for tuning cardiac threshold response to common inflammatory stressors.

Prenatal microarray analysis in right aortic arch—a retrospective cohort study and review of the literature

Objective:To examine the risk for clinically significant chromosomal microarray analysis (CMA) findings in fetal right aortic arch (RAA).Methods:Data from all CMA analyses performed owing to isolated RAA reported to the Israeli Ministry of Health between January 2013 and September 2016 were evaluated retrospectively. Risk for abnormal CMA findings was compared with two control populations, based on both previously described 9272 pregnancies with normal ultrasound, and on a local cohort of 5541 pregnancies undergoing CMA testing owing to maternal request. In addition, Pubmed database search was conducted for original researches examining this issue.Results:Of 94 CMA analyses performed owing to isolated RAA, six (6.4%) pathogenic findings were detected (47,XX + 21; 45,X; two 22q11.2 microdeletions; 10p15.3 microdeletion and 16p11.2 duplication). Compared with control groups, an isolated RAA yielded a significantly increased relative risk for abnormal CMA results. Literature search yielded two additional retrospective studies describing microarray testing in RAA and encompassing 57 cases. The overall risk for clinically significant CMA findings was 6.62% (10/151).Conclusions:CMA testing is indicated in cases of prenatal isolated RAA, even in the era of advanced sonographic equipment, routine biochemical screening for Down syndrome and available non-invasive prenatal testing.

Chromosomal microarray findings in pregnancies with an isolated pelvic kidney

Abstract Objective To examine the risk for abnormal chromosomal microarray analysis (CMA) results among fetuses with an apparently isolated pelvic kidney. Methods Data from all CMA analyses performed due to an isolated pelvic kidney reported to the Israeli Ministry of Health between January 2013 and September 2016 were retrospectively obtained. Risk estimation was performed comparing the rate of abnormal observed CMA findings to the general population risk, based on a systematic review encompassing 9272 cases and on local data of 5541 cases. Results Of 120 pregnancies with an isolated pelvic kidney, two gain-of-copy number variants suggesting microduplication syndromes were demonstrated (1.67%). In addition, three variants of unknown significance were detected (2.5%). Conclusion The risk for clinically significant CMA findings among pregnancies with an isolated single pelvic kidney was not significantly different compared to both control populations. The results of our study question the practice of routine CMA analysis in fetuses with an isolated pelvic kidney.