Mordechai Shohat

Prevalence and Evolutionary Origins of the del(GJB6-D13S1830) Mutation in the DFNB1 Locus in Hearing-Impaired Subjects: A Multicenter Study

Mutations in GJB2, the gene encoding connexin-26 at the DFNB1 locus on 13q12, are found in as many as 50% of subjects with autosomal recessive, nonsyndromic prelingual hearing impairment. However, genetic diagnosis is complicated by the fact that 10%-50% of affected subjects with GJB2 mutations carry only one mutant allele. Recently, a deletion truncating the GJB6 gene (encoding connexin-30), near GJB2 on 13q12, was shown to be the accompanying mutation in approximately 50% of these deaf GJB2 heterozygotes in a cohort of Spanish patients, thus becoming second only to 35delG at GJB2 as the most frequent mutation causing prelingual hearing impairment in Spain. Here, we present data from a multicenter study in nine countries that shows that the deletion is present in most of the screened populations, with higher frequencies in France, Spain, and Israel, where the percentages of unexplained GJB2 heterozygotes fell to 16.0%-20.9% after screening for the del(GJB6-D13S1830) mutation. Our results also suggest that additional mutations remain to be identified, either in DFNB1 or in other unlinked genes involved in epistatic interactions with GJB2. Analysis of haplotypes associated with the deletion revealed a founder effect in Ashkenazi Jews and also suggested a common founder for countries in Western Europe. These results have important implications for the diagnosis and counseling of families with DFNB1 deafness.

The genetic architecture of Down syndrome phenotypes revealed by high-resolution analysis of human segmental trisomies

Down syndrome (DS), or trisomy 21, is a common disorder associated with several complex clinical phenotypes. Although several hypotheses have been put forward, it is unclear as to whether particular gene loci on chromosome 21 (HSA21) are sufficient to cause DS and its associated features. Here we present a high-resolution genetic map of DS phenotypes based on an analysis of 30 subjects carrying rare segmental trisomies of various regions of HSA21. By using state-of-the-art genomics technologies we mapped segmental trisomies at exon-level resolution and identified discrete regions of 1.8–16.3 Mb likely to be involved in the development of 8 DS phenotypes, 4 of which are congenital malformations, including acute megakaryocytic leukemia, transient myeloproliferative disorder, Hirschsprung disease, duodenal stenosis, imperforate anus, severe mental retardation, DS-Alzheimer Disease, and DS-specific congenital heart disease (DSCHD). Our DS-phenotypic maps located DSCHD to a <2-Mb interval. Furthermore, the map enabled us to present evidence against the necessary involvement of other loci as well as specific hypotheses that have been put forward in relation to the etiology of DS—i.e., the presence of a single DS consensus region and the sufficiency of DSCR1 and DYRK1A, or APP, in causing several severe DS phenotypes. Our study demonstrates the value of combining advanced genomics with cohorts of rare patients for studying DS, a prototype for the role of copy-number variation in complex disease.

Mutant Adenosine Deaminase 2 in a Polyarteritis Nodosa Vasculopathy

BACKGROUND Polyarteritis nodosa is a systemic necrotizing vasculitis with a pathogenesis that is poorly understood. We identified six families with multiple cases of systemic and cutaneous polyarteritis nodosa, consistent with autosomal recessive inheritance. In most cases, onset of the disease occurred during childhood. METHODS We carried out exome sequencing in persons from multiply affected families of Georgian Jewish or German ancestry. We performed targeted sequencing in additional family members and in unrelated affected persons, 3 of Georgian Jewish ancestry and 14 of Turkish ancestry. Mutations were assessed by testing their effect on enzymatic activity in serum specimens from patients, analysis of protein structure, expression in mammalian cells, and biophysical analysis of purified protein. RESULTS In all the families, vasculitis was caused by recessive mutations in CECR1, the gene encoding adenosine deaminase 2 (ADA2). All the Georgian Jewish patients were homozygous for a mutation encoding a Gly47Arg substitution, the German patients were compound heterozygous for Arg169Gln and Pro251Leu mutations, and one Turkish patient was compound heterozygous for Gly47Val and Trp264Ser mutations. In the endogamous Georgian Jewish population, the Gly47Arg carrier frequency was 0.102, which is consistent with the high prevalence of disease. The other mutations either were found in only one family member or patient or were extremely rare. ADA2 activity was significantly reduced in serum specimens from patients. Expression in human embryonic kidney 293T cells revealed low amounts of mutant secreted protein. CONCLUSIONS Recessive loss-of-function mutations of ADA2, a growth factor that is the major extracellular adenosine deaminase, can cause polyarteritis nodosa vasculopathy with highly varied clinical expression. (Funded by the Shaare Zedek Medical Center and others.).

Mutation in TRMU Related to Transfer RNA Modification Modulates the Phenotypic Expression of the Deafness-Associated Mitochondrial 12S Ribosomal RNA Mutations

The human mitochondrial 12S ribosomal RNA (rRNA) A1555G mutation has been associated with aminoglycoside-induced and nonsyndromic deafness in many families worldwide. Our previous investigation revealed that the A1555G mutation is a primary factor underlying the development of deafness but is not sufficient to produce a deafness phenotype. However, it has been proposed that nuclear-modifier genes modulate the phenotypic manifestation of the A1555G mutation. Here, we identified the nuclear-modifier gene TRMU, which encodes a highly conserved mitochondrial protein related to transfer RNA (tRNA) modification. Genotyping analysis of TRMU in 613 subjects from 1 Arab-Israeli kindred, 210 European (Italian pedigrees and Spanish pedigrees) families, and 31 Chinese pedigrees carrying the A1555G or the C1494T mutation revealed a missense mutation (G28T) altering an invariant amino acid residue (A10S) in the evolutionarily conserved N-terminal region of the TRMU protein. Interestingly, all 18 Arab-Israeli/Italian-Spanish matrilineal relatives carrying both the TRMU A10S and 12S rRNA A1555G mutations exhibited prelingual profound deafness. Functional analysis showed that this mutation did not affect importation of TRMU precursors into mitochondria. However, the homozygous A10S mutation leads to a marked failure in mitochondrial tRNA metabolisms, specifically reducing the steady-state levels of mitochondrial tRNA. As a consequence, these defects contribute to the impairment of mitochondrial-protein synthesis. Resultant biochemical defects aggravate the mitochondrial dysfunction associated with the A1555G mutation, exceeding the threshold for expressing the deafness phenotype. These findings indicate that the mutated TRMU, acting as a modifier factor, modulates the phenotypic manifestation of the deafness-associated 12S rRNA mutations.

Fragile-X Carrier Screening and the Prevalence of Premutation and Full-Mutation Carriers in Israel

Fragile-X syndrome is caused by an unstable CGG trinucleotide repeat in the FMR1 gene at Xq27. Intermediate alleles (51-200 repeats) can undergo expansion to the full mutation on transmission from mother to offspring. To evaluate the effectiveness of a fragile-X carrier-screening program, we tested 14,334 Israeli women of child-bearing age for fragile-X carrier status between 1992 and 2000. These women were either preconceptional or pregnant and had no family history of mental retardation. All those found to be carriers of premutation or full-mutation alleles were offered genetic counseling and also prenatal diagnosis, if applicable. We identified 207 carriers of an allele with >50 repeats, representing a prevalence of 1:69. There were 127 carriers with >54 repeats, representing a prevalence of 1:113. Three asymptomatic women carried the fully mutated allele. Among the premutation and full-mutation carriers, 177 prenatal diagnoses were performed. Expansion occurred in 30 fetuses, 5 of which had an expansion to the full mutation. On the basis of these results, the expected number of avoided patients born to women identified as carriers, the cost of the test in this study (U.S.

The prevalence and expression of inherited connexin 26 mutations associated with nonsyndromic hearing loss in the Israeli population.

100), and the cost of lifetime care for a mentally retarded person (>

Targeted genomic capture and massively parallel sequencing to identify genes for hereditary hearing loss in middle eastern families

350,000), screening was calculated to be cost-effective. Because of the high prevalence of fragile-X premutation or full-mutation alleles, even in the general population, and because of the cost-effectiveness of the program, we recommend that screening to identify female carriers should be carried out on a wide scale.

Obsessive-compulsive disorder in patients with velocardiofacial (22q11 deletion) syndrome

Abstract. Connexin 26 (GJB2) mutations lead to hearing loss in a significant proportion of all populations studied so far, despite the fact that at least 50 other genes are also associated with hearing loss. The entire coding region of connexin 26 was sequenced in 75 hearing impaired children and adults in Israel in order to determine the percentage of hearing loss attributed to connexin 26 and the types of mutations in this population. Age of onset in the screened population was both prelingual and postlingual, with hearing loss ranging from moderate to profound. Almost 39% of all persons tested harbored GJB2 mutations, the majority of which were 35delG and 167delT mutations. A novel mutation, involving both a deletion and insertion, 51del12insA, was identified in a family originating from Uzbekistan. Several parameters were examined to establish whether genotype-phenotype correlations exist, including age of onset, severity of hearing loss and audiological characteristics, including pure-tone audiometry, tympanometry, auditory brainstem response (ABR), and transient evoked otoacoustic emissions (TEOAE). All GJB2 mutations were associated with prelingual hearing loss, though severity ranged from moderate to profound, with variability even among hearing impaired siblings. We have not found a significant difference in hearing levels between individuals with 35delG and 167delT mutations. Our results suggest that, in Israel, clinicians should first screen for the common 167delT and 35delG mutations by simple and inexpensive restriction enzyme analysis, although if these are not found, sequencing should be done to rule out additional mutations due to the ethnic diversity in this region.

Mutations in NDUFAF3 (C3ORF60), Encoding an NDUFAF4 (C6ORF66)-Interacting Complex I Assembly Protein, Cause Fatal Neonatal Mitochondrial Disease

BackgroundIdentification of genes responsible for medically important traits is a major challenge in human genetics. Due to the genetic heterogeneity of hearing loss, targeted DNA capture and massively parallel sequencing are ideal tools to address this challenge. Our subjects for genome analysis are Israeli Jewish and Palestinian Arab families with hearing loss that varies in mode of inheritance and severity.ResultsA custom 1.46 MB design of cRNA oligonucleotides was constructed containing 246 genes responsible for either human or mouse deafness. Paired-end libraries were prepared from 11 probands and bar-coded multiplexed samples were sequenced to high depth of coverage. Rare single base pair and indel variants were identified by filtering sequence reads against polymorphisms in dbSNP132 and the 1000 Genomes Project. We identified deleterious mutations in CDH23, MYO15A, TECTA, TMC1, and WFS1. Critical mutations of the probands co-segregated with hearing loss. Screening of additional families in a relevant population was performed. TMC1 p.S647P proved to be a founder allele, contributing to 34% of genetic hearing loss in the Moroccan Jewish population.ConclusionsCritical mutations were identified in 6 of the 11 original probands and their families, leading to the identification of causative alleles in 20 additional probands and their families. The integration of genomic analysis into early clinical diagnosis of hearing loss will enable prediction of related phenotypes and enhance rehabilitation. Characterization of the proteins encoded by these genes will enable an understanding of the biological mechanisms involved in hearing loss.

Autosomal Recessive Ichthyosis with Hypotrichosis Caused by a Mutation in ST14, Encoding Type II Transmembrane Serine Protease Matriptase

The study of neurogenetic microdeletion syndromes provides an insight into the developmental psychopathology of psychiatric disorders. The aim of the study was to evaluate the prevalence of psychiatric disorders, especially obsessive‐compulsive disorder (OCD), in patients with velocardiofacial syndrome (VCFS), a 22q11 microdeletion syndrome. Forty‐three subjects with VCFS of mean age 18.3 ± 10.6 years were comprehensively assessed using semi‐structured psychiatric interview and the Yale–Brown obsessive compulsive scale (Y‐BOCS). Best estimate diagnoses were made on the basis of information gathered from subjects, parents, teachers, and social workers. Fourteen VCFS subjects (32.6%) met the DSM‐IV criteria for OCD. OCD had an early age of onset and generally responded to fluoxetine treatment. It was not related to mental retardation. The most common obsessive‐compulsive symptoms were contamination, aggression, somatic worries, hoarding, repetitive questions, and cleaning. Sixteen of the 43 patients (37.2%) had attention‐deficit/hyperactivity disorder (ADHD), and 7 (16.2%) had psychotic disorder. The results of our study suggest that there is a strong association between VCFS and early‐onset OCD. This finding may be significant in the understanding of the underlying genetic basis of OCD.