Biallelic Loss-of-Function Variants in BICD1 Are Associated with Peripheral Neuropathy and Hearing Loss

Hearing loss and peripheral neuropathy are two clinical entities that are genetically and phenotypically heterogeneous and sometimes co-occurring. Using exome sequencing and targeted segregation analysis, we investigated the genetic etiology of peripheral neuropathy and hearing loss in a large Ashkenazi Jewish family. Moreover, we assessed the production of the candidate protein via western blotting of lysates from fibroblasts from an affected individual and an unaffected control. Pathogenic variants in known disease genes associated with hearing loss and peripheral neuropathy were excluded. A homozygous frameshift variant in the BICD1 gene, c.1683dup (p.(Arg562Thrfs*18)), was identified in the proband and segregated with hearing loss and peripheral neuropathy in the family. The BIDC1 RNA analysis from patient fibroblasts showed a modest reduction in gene transcripts compared to the controls. In contrast, protein could not be detected in fibroblasts from a homozygous c.1683dup individual, whereas BICD1 was detected in an unaffected individual. Our findings indicate that bi-allelic loss-of-function variants in BICD1 are associated with hearing loss and peripheral neuropathy. Definitive evidence that bi-allelic loss-of-function variants in BICD1 cause peripheral neuropathy and hearing loss will require the identification of other families and individuals with similar variants with the same phenotype.

Expanding the phenotypic spectrum of COLEC10-Related 3MC syndrome: A glimpse into COLEC10-Related 3MC syndrome in the Ashkenazi Jewish population

Bi-allelic variants in COLEC11 and MASP1 have been associated with 3MC syndrome, a clinical entity made of up four rare autosomal recessive disorders: Carnevale, Mingarelli, Malpuech, and Michels syndromes, characterized by variable expression of facial dysmorphia, cleft lip/palate, postnatal growth deficiency, hearing loss, cognitive impairment, craniosynostosis, radioulnar synostosis, and genital and vesicorenal anomalies. More recently, bi-allelic variants in COLEC10 have been described to be associated with 3MC syndrome. Syndromic features seen in 3MC syndrome are thought to be due to disruption of the chemoattractant properties that influence neural crest cell migration. We identified nine individuals from five families of Ashkenazi Jewish descent with homozygosity of the c.311G > T (p.Gly104Val) variant in COLEC10 and phenotype consistent with 3MC syndrome. Carrier frequency was calculated among 52,278 individuals of Jewish descent. Testing revealed 400 carriers out of 39,750 individuals of Ashkenazi Jewish descent, giving a carrier frequency of 1 in 99 or 1.01%. Molecular protein modeling suggested that the p.Gly104Val substitution alters local conformation. The c.311G > T (p.Gly104Val) variant likely represents a founder variant, and homozygosity is associated with features of 3MC syndrome. 3MC syndrome should be in the differential diagnosis for individuals with short stature, radioulnar synostosis, cleft lip and cleft palate.

Identification of Novel and Recurrent Variants in MYO15A in Ashkenazi Jewish Patients With Autosomal Recessive Nonsyndromic Hearing Loss

Hearing loss is a genetically and phenotypically heterogeneous disorder. The purpose of this study was to determine the genetic cause underlying hearing loss in four Ashkenazi Jewish families. We screened probands from each family using a combination of targeted mutation screening and exome sequencing to identifiy the genetic cause of hearing loss in each family. We identified four variants in MYO15A, two novel variants never previously linked to deafness (c.7212+5G>A and p.Leu2532ArgfsTer37) and two recurrent variants (p.Tyr2684His and p.Gly3287Gly). One family showed locus heterogeneity, segregrating two genetic forms of hearing loss. Mini-gene assays revealed the c.7212+5G>A variant results in abnormal splicing and is most likely a null allele. We show that families segregrating the p.Gly3287Gly variant show both inter and intra-familial phenotypic differences. These results add to the list of MYO15A deafness-causing variants, further confirm the pathogenicity of the p.Gly3287Gly variant and shed further light on the genetic etiology of hearing loss in the Ashkenazi Jewish population.

Biallelic variants of ATP13A3 cause dose-dependent childhood-onset pulmonary arterial hypertension characterised by extreme morbidity and mortality

Background

The molecular genetic basis of pulmonary arterial hypertension (PAH) is heterogeneous, with at least 26 genes displaying putative evidence for disease causality. Heterozygous variants in the ATP13A3 gene were recently identified as a new cause of adult-onset PAH. However, the contribution of ATP13A3 risk alleles to child-onset PAH remains largely unexplored.

Methods and results

We report three families with a novel, autosomal recessive form of childhood-onset PAH due to biallelic ATP13A3 variants. Disease onset ranged from birth to 2.5 years and was characterised by high mortality. Using genome sequencing of parent–offspring trios, we identified a homozygous missense variant in one case, which was subsequently confirmed to cosegregate with disease in an affected sibling. Independently, compound heterozygous variants in ATP13A3 were identified in two affected siblings and in an unrelated third family. The variants included three loss of function variants (two frameshift, one nonsense) and two highly conserved missense substitutions located in the catalytic phosphorylation domain. The children were largely refractory to treatment and four died in early childhood. All parents were heterozygous for the variants and asymptomatic.

Conclusion

Our findings support biallelic predicted deleterious ATP13A3 variants in autosomal recessive, childhood-onset PAH, indicating likely semidominant dose-dependent inheritance for this gene.

Further Delineation of the Clinical and Pathologic Features of HIKESHI-Related Hypomyelinating Leukodystrophy

BACKGROUND

A recurrent homozygous missense variant, c.160G>C;p.(Val54Leu) in HIKESHI, was found to cause a hypomyelinating leukodystrophy with high frequency in the Ashkenazi Jewish population. We provide extended phenotypic classification of this disorder based on clinical history of a further seven affected individuals, assess carrier frequency in the Ashkenazi Jewish population, and provide a neuropathological study.

METHODS

Clinical information, neuroimaging, and biosamples were collected. Brain autopsy was performed for one case.

RESULTS

Individuals with HIKESHI-related disease share common clinical features: early axial hypotonia evolving to dystonia or with progressive spasticity, hyperreflexia and clonus, feeding difficulties with poor growth, and nystagmus. Severe morbidity or death during febrile illness occurred in five of the nine affected individuals. Magnetic resonance images of seven patients were analyzed and demonstrated diffuse hypomyelination and thin corpus callosum. Genotyping data of more than 125,000 Ashkenazi Jewish individuals revealed a carrier frequency of 1 in 216. Gross pathology examination in one case revealed abnormal white matter. Microscopically, there was a near-total absence of myelin with a relative preservation of axons. The cerebral white matter showed several reactive astrocytes and microglia.

CONCLUSIONS

We provide pathologic evidence for a primary disorder of the myelin in HIKESHI-related leukodystrophy. These findings are consistent with the hypomyelination seen in brain magnetic resonance imaging and with the clinical features of early-onset spastic/dystonic quadriplegia and nystagmus. The high carrier rate of the recurrent variant seen in the Ashkenazi Jewish population requires increased attention to screening and diagnosis of this condition, particularly in this population.

Recommendation of premarital genetic screening in the Syrian Jewish community based on mutation carrier frequencies within Syrian Jewish cohorts

Background

There is a paucity of information available regarding the carrier frequency for autosomal recessive pathogenic variants among Syrian Jews. This report provides data to support carrier screening for a group of autosomal recessive conditions among Syrian Jews based on the population frequency of 40 different pathogenic variants in a cohort of over 3800 individuals with Syrian Jewish ancestry.

Methods

High throughput PCR amplicon sequencing was used to genotype 40 disease‐causing variants in 3840 and 5279 individuals of Syrian and Iranian Jewish ancestry, respectively. These data were compared with Ashkenazi Jewish carrier frequencies for the same variants, based on roughly 370,000 Ashkenazi Jewish individuals in the Dor Yeshorim database.

Results

Carrier screening identified pathogenic variants shared among Syrian, Iranian, and Ashkenazi Jewish groups. In addition, alleles unique to each group were identified. Importantly, 8.2% of 3401 individuals of mixed Syrian Jewish ancestry were carriers for at least one pathogenic variant.

Conclusion

The findings of this study support the clinical usefulness of premarital genetic screening for individuals with Syrian Jewish ancestry to reduce the incidence of autosomal recessive disease among persons with Syrian Jewish heritage.

A synonymous variant in MYO15A enriched in the Ashkenazi Jewish population causes autosomal recessive hearing loss due to abnormal splicing

Nonsyndromic hearing loss is genetically heterogeneous. Despite comprehensive genetic testing, many cases remain unsolved because the clinical significance of identified variants is uncertain or because biallelic pathogenic variants are not identified for presumed autosomal recessive cases. Common synonymous variants are often disregarded. Determining the pathogenicity of synonymous variants may improve genetic diagnosis. We report a synonymous variant c.9861 C > T/p.(Gly3287=) in MYO15A in homozygosity or compound heterozygosity with another pathogenic or likely pathogenic MYO15A variant in 10 unrelated families with nonsyndromic sensorineural hearing loss. Biallelic variants in MYO15A were identified in 21 affected and were absent in 22 unaffected siblings. A mini-gene assay confirms that the synonymous variant leads to abnormal splicing. The variant is enriched in the Ashkenazi Jewish population. Individuals carrying biallelic variants involving c.9861 C > T often exhibit progressive post-lingual hearing loss distinct from the congenital profound deafness typically associated with biallelic loss-of-function MYO15A variants. This study establishes the pathogenicity of the c.9861 C > T variant in MYO15A and expands the phenotypic spectrum of MYO15A-related hearing loss. Our work also highlights the importance of multicenter collaboration and data sharing to establish the pathogenicity of a relatively common synonymous variant for improved diagnosis and management of hearing loss.

Utilizing ethnic-specific differences in minor allele frequency to recategorize reported pathogenic deafness variants

Ethnic-specific differences in minor allele frequency impact variant categorization for genetic screening of nonsyndromic hearing loss (NSHL) and other genetic disorders. We sought to evaluate all previously reported pathogenic NSHL variants in the context of a large number of controls from ethnically distinct populations sequenced with orthogonal massively parallel sequencing methods. We used HGMD, ClinVar, and dbSNP to generate a comprehensive list of reported pathogenic NSHL variants and re-evaluated these variants in the context of 8,595 individuals from 12 populations and 6 ethnically distinct major human evolutionary phylogenetic groups from three sources (Exome Variant Server, 1000 Genomes project, and a control set of individuals created for this study, the OtoDB). Of the 2,197 reported pathogenic deafness variants, 325 (14.8%) were present in at least one of the 8,595 controls, indicating a minor allele frequency (MAF) > 0.00006. MAFs ranged as high as 0.72, a level incompatible with pathogenicity for a fully penetrant disease like NSHL. Based on these data, we established MAF thresholds of 0.005 for autosomal-recessive variants (excluding specific variants in GJB2) and 0.0005 for autosomal-dominant variants. Using these thresholds, we recategorized 93 (4.2%) of reported pathogenic variants as benign. Our data show that evaluation of reported pathogenic deafness variants using variant MAFs from multiple distinct ethnicities and sequenced by orthogonal methods provides a powerful filter for determining pathogenicity. The proposed MAF thresholds will facilitate clinical interpretation of variants identified in genetic testing for NSHL. All data are publicly available to facilitate interpretation of genetic variants causing deafness.

Carrier screening of RTEL1 mutations in the Ashkenazi Jewish population

Hoyeraal-Hreidarsson syndrome (HH) is a clinically severe variant of dyskeratosis congenita (DC), characterized by cerebellar hypoplasia, microcephaly, intrauterine growth retardation, and severe immunodeficiency in addition to features of DC. Germline mutations in the RTEL1 gene have recently been identified as causative of HH. In this study, the carrier frequency for five RTEL1 mutations that occurred in individuals of Ashkenazi Jewish descent was investigated in order to advise on including them in existing clinical mutation panels for this population. Our screening showed that the carrier frequency for c.3791G>A (p.R1264H) was higher than expected, 1% in the Ashkenazi Orthodox and 0.45% in the general Ashkenazi Jewish population. Haplotype analyses suggested the presence of a common founder. We recommend that the c.3791G>A RTEL1 mutation be considered for inclusion in carrier screening panels in the Ashkenazi population.

A founder mutation in the TCIRG1 gene causes osteopetrosis in the Ashkenazi Jewish population

Osteopetrosis is a rare and heterogeneous genetic disorder characterized by dense bone mass that is a consequence of defective osteoclast function and/or development. Autosomal recessive osteopetrosis (ARO) is the most severe form and is often fatal within the first years of life; early hematopoietic stem cell transplant (HSCT) remains the only curative treatment for ARO. The majority of the ARO-causing mutations are located in the TCIRG1 gene. We report here the identification and characterization of an A to T transversion in the fourth base of the intron 2 donor splice site (c.117+4A→T) in TCIRG1, a mutation not previously seen in the Ashkenazi Jewish (AJ) population. Analysis of a random sample of individuals of AJ descent revealed a carrier frequency of approximately 1 in 350. Genotyping of five loci adjacent to the c.117+4A→T-containing TCIRG1 allele revealed that the presence of this mutation in the AJ population is due to a single founder. The identification of this mutation will enable population carrier testing and will facilitate the identification and treatment of individuals homozygous for this mutation.

High-throughput carrier screening using TaqMan allelic discrimination

Members of the Ashkenazi Jewish community are at an increased risk for inheritance of numerous genetic diseases such that carrier screening is medically recommended. This paper describes the development and evaluation of 30 TaqMan allelic discrimination qPCR assays for 29 mutations on 2 different high-throughput platforms. Four of these mutations are in the GBA gene and are successfully examined using short amplicons due to the qualitative nature of TaqMan allelic discrimination. Two systems were tested for their reliability (call rate) and consistency with previous diagnoses (diagnostic accuracy) indicating a call rate of 99.04% and a diagnostic accuracy of 100% (+/−0.00%) from one platform, and a call rate of 94.66% and a diagnostic accuracy of 93.35% (+/−0.29%) from a second for 9,216 genotypes. Results for mutations tested at the expected carrier frequency indicated a call rate of 97.87% and a diagnostic accuracy of 99.96% (+/−0.05%). This study demonstrated the ability of a high throughput qPCR methodology to accurately and reliably genotype 29 mutations in parallel. The universally applicable nature of this technology provides an opportunity to increase the number of mutations that can be screened simultaneously, and reduce the cost and turnaround time for accommodating newly identified and clinically relevant mutations.

Splice site, frameshift, and chimeric GFAP mutations in Alexander disease

Alexander disease (AxD) is a usually fatal astrogliopathy primarily caused by mutations in the gene encoding glial fibrillary acidic protein (GFAP), an intermediate filament protein expressed in astrocytes. We describe three patients with unique characteristics, and whose mutations have implications for AxD diagnosis and studies of intermediate filaments. Patient 1 is the first reported case with a noncoding mutation. The patient has a splice site change producing an in-frame deletion of exon 4 in about 10% of the transcripts. Patient 2 has an insertion and deletion at the extreme end of the coding region, resulting in a short frameshift. In addition, the mutation was found in buccal DNA but not in blood DNA, making this patient the first reported chimera. Patient 3 has a single-base deletion near the C-terminal end of the protein, producing a short frameshift. These findings recommend inclusion of intronic splice site regions in genetic testing for AxD, indicate that alteration of only a small fraction of GFAP can produce disease, and provide caution against tagging intermediate filaments at their C-terminal end for cell biological investigations.

[The pathogenesis of periodontal disease: a paradigm shift]

Periodontitis is a family of related diseases that differ in etiology, natural history, disease progression and response to therapy, but have a common underlying chain of events, thatareinfluenced by disease modifiers. The clinical manifestations observed are a result of the complex interplay of these factors. The pathogenesis of human periodontitis was placed on a rational footing for the first time by Page & Schroeder in 1976 and the general principles and the overall conclusions reached in that article are still largely acceptable today. Still, an enormous amount has been learned about all aspects of human periodontitis, including its pathogenesis, since 1976. A critical evaluation of the literature regarding the complex relationship between the microbial factor, the host factor and the occurrence of a disease, might be leading us over a surge of a paradigm shift in our understanding the pathogenesis of the disease. It is well acknowledged that while the etiology of periodontitis is bacterial, the pathogenesis is inflammatory. The understanding of regulation of inflammation in periodontitis is far from complete; however, as the understanding of periodontal inflammation increases, the current understanding of the microbiology of periodontitis becomes less clear. While we think we know that bacteria initiate the disease, the role of specific bacteria is still unknown. The current knowledge of the microbiology of periodontitis is based on large cross-sectional and association studies. Periodontitis is seen as the direct consequence of bacterial invasion and is regarded as an infectious disease. It is however, not possible to draw cause and- effect inferences from these studies. One might state that the inflammation precedes the overgrowth of the bacteria. In this scenario, the initiator of the disease might be early, gram-positive colonizers that elicit a profound inflammatory response in the susceptible host. The implication of that paradigm shift outlined above is that periodontitis is an inflammatory disease, and in that case the primary target of pharmacotherapy should be the inflammation, rather than the bacteria. Still, the question to be asked and investigated is whether dampening of the inflammatory response in certain individuals susceptible to periodontitis might prevent development of disease. This is a question yet to be answered.

A novel mutation in NDUFS4 causes Leigh syndrome in an Ashkenazi Jewish family

Leigh syndrome is a neurodegenerative disorder of infancy or childhood generally due to mutations in nuclear or mitochondrial genes involved in mitochondrial energy metabolism. We performed linkage analysis in an Ashkenazi Jewish (AJ) family without consanguinity with three affected children. Linkage to microsatellite markers D5S1969 and D5S407 led to evaluation of the complex I gene NDUFS4, in which we identified a novel homozygous c.462delA mutation that disrupts the reading frame. The resulting protein lacks a cAMP-dependent protein kinase phosphorylation site required for activation of mitochondrial respiratory chain complex I. In a random sample of 5000 healthy AJ individuals, the carrier frequency of the NDUFS4 mutation c.462delA was 1 in 1000, suggesting that it should be considered in all AJ patients with Leigh syndrome.

Growth-plate chondrocytes respond to 17beta-estradiol with sex-specific increases in IP3 and intracellular calcium ion signalling via a capacitative entry mechanism

17Beta-estradiol (E(2)) regulates growth-plate chondrocyte differentiation in a gender and cell maturation-dependent manner via classic nuclear receptors ERalpha and ERbeta, and membrane-associated signalling. Here we show that sex-specific effects of E(2) involve changes in intracellular calcium concentration (ICCC). Resting-zone chondrocytes (RC) and growth-zone chondrocytes (GC) were isolated from costochondral cartilage of male and female rats. Confluent cultures were treated with 10(-8)M E(2) or 17alpha-estradiol in the presence of high and low extracellular Ca(2+) concentration. The ICCC was determined using laser scanning confocal microscopy to measure changes in Fluo-4 fluorescence every 5s for a total of 500s. E(2) increased ICCC in the cells from female rats but had no effect on ICCC in male cells. The effect was rapid (peak at 140s) and stereospecific. E(2) increased ICCC in RC and GC chondrocytes but the effect was greater in RC cells. Low Ca(2+) media did not abolish the E(2)-dependent ICCC elevation, nor did inclusion of verapamil, which inhibits Ca(2+) channels on the cell membrane. Thapsigargin reduced the effect of E(2) on ICCC, showing that Ca(2+) pumps on the endoplasmic reticulum were involved. Pre-treatment of the cells with the ER antagonist ICI 182780 did not alter the stimulatory effect of E(2), suggesting that traditional estrogen receptor mechanisms do not play a role. E(2) caused rapid production of inositol-1,4,5-trisphosphate (IP3) and diacylglycerol (DAG) but only in female cells, and the effect was greater in RC chondrocytes. These results indicate that E(2) regulates ICCC in a sex-specific and cell maturation state-dependent manner. The mechanism is membrane-associated and is mediated by PLC-dependent IP3 production and release of Ca(2+) from the endoplasmic reticulum.

Mutation frequencies for glycogen storage disease Ia in the Ashkenazi Jewish population

Glycogen storage disease type Ia (GSDIa) is a severe autosomal recessive disorder caused by deficiency of the enzyme D-glucose-6-phosphatase (G6Pase). While numerous mutations have been found in cosmopolitan European populations, Ashkenazi Jewish (AJ) patients appear to primarily carry the R83C mutation, but possibly also the Q347X mutation found generally in Caucasians. To determine the frequency for both these mutations in the AJ population, we tested 20,719 AJ subjects for the R83C mutation and 4,290 subjects for the Q347X mutation. We also evaluated the mutation status of 30 AJ GSDIa affected subjects. From the carrier screening, we found 290 subjects with R83C, for a carrier frequency for this mutation of 1.4%. This carrier frequency translates into a predicted disease prevalence of 1 in 20,000, five times higher than for the general Caucasian population, confirming a founder effect and elevated frequency of GSDIa in the AJ population. We observed no carriers of the Q347X mutation. Among the 30 GSDIa affected AJ subjects, all were homozygous for R83C. These results indicate that R83C is the only prevalent mutation for GSDIa in the Ashkenazi population.

Premarital and prenatal screening for cystic fibrosis: experience in the Ashkenazi Jewish population

PURPOSE

Since the early 1990s, Dor Yeshorim (DY) and the Mount Sinai School of Medicine (MSSM) have conducted premarital and prenatal carrier screening for cystic fibrosis (CF) in the Ashkenazi Jewish (AJ) population as part of their genetic testing programs, respectively. Together, over 170,000 screenees have been tested. In this study, we report the CF mutation frequencies in over 110,000 screenees who reportedly were of 100% AJ descent from the DY program and MSSM. In addition, the CF mutation frequencies in a group of > 7,000 screenees for AJ diseases who were of < 100% AJ descent are reported.

METHODS

Testing for CF mutations was performed by either PCR and restriction digestion or ASO hybridization analyses at MSSM or sent to various academic and commercial laboratories by DY.

RESULTS

The overall (and individual) carrier frequency for the five common AJ mutations, W1282X (0.020), DeltaF508 (0.012), G542X (0.0024), 3849+10kb C>T (0.0020), and N1303K (0.0016), among screenees who were 100% AJ was 1 in 26; when D1152H and the rare 1717-1G>A were included, the overall carrier frequency increased to approximately 1 in 23. In four families with D1152H, five compound heterozygotes for D1152H and W1282X (n = 2), DeltaF508 (1) or 3849+10kb C>T (1) were identified. In contrast, the carrier frequency for screenees reporting < 100% AJ descent was approximately 1 in 30 for the seven mutations.

CONCLUSIONS

The carrier frequency for five common CF mutations in a large 100% AJ sample increased from 1 in 26 to 1 in 23 when D1152H was included in the panel. Addition of D1152H to mutation panels when screening the AJ population should be considered because compound heterozygosity is associated with a variable disease phenotype. Further studies to delineate the phenotype of CF patients with this mutation are needed.

Nemaline myopathy in the Ashkenazi Jewish population is caused by a deletion in the nebulin gene

Nemaline myopathy (NM) is a neuromuscular disorder that is clinically diverse and can be attributed to mutations in any of several genes. The Ashkenazi Jewish population, which represents a relatively genetically homogeneous group, has an increased frequency of several genetic disorders and has been the beneficiary of genetic screening programs that have reduced the incidence of these diseases. The identification of individuals with NM in this population has prompted a study of its cause. Our study has revealed that five NM patients from five families bear an identical 2,502-bp deletion that lies in the nebulin gene and that includes exon 55 and parts of introns 54 and 55. The absence of this exon results in the generation of a transcript that encodes 35 fewer amino acids. An analysis of the gene frequency of this mutation in a random sample of 4,090 Ashkenazi Jewish individuals has revealed a carrier frequency of one in 108.

Geographic distribution of disease mutations in the Ashkenazi Jewish population supports genetic drift over selection

The presence of four lysosomal storage diseases (LSDs) at increased frequency in the Ashkenazi Jewish population has suggested to many the operation of natural selection (carrier advantage) as the driving force. We compare LSDs and nonlysosomal storage diseases (NLSDs) in terms of the number of mutations, allele-frequency distributions, and estimated coalescence dates of mutations. We also provide new data on the European geographic distribution, in the Ashkenazi population, of seven LSD and seven NLSD mutations. No differences in any of the distributions were observed between LSDs and NLSDs. Furthermore, no regular pattern of geographic distribution was observed for LSD versus NLSD mutations-with some being more common in central Europe and others being more common in eastern Europe, within each group. The most striking disparate pattern was the geographic distribution of the two primary Tay-Sachs disease mutations, with the first being more common in central Europe (and likely older) and the second being exclusive to eastern Europe (primarily Lithuania and Russia) (and likely much younger). The latter demonstrates a pattern similar to two other recently arisen Lithuanian mutations, those for torsion dystonia and familial hypercholesterolemia. These observations provide compelling support for random genetic drift (chance founder effects, one approximately 11 centuries ago that affected all Ashkenazim and another approximately 5 centuries ago that affected Lithuanians), rather than selection, as the primary determinant of disease mutations in the Ashkenazi population.

Familial dysautonomia is caused by mutations of the IKAP gene

The defective gene DYS, which is responsible for familial dysautonomia (FD) and has been mapped to a 0.5-cM region on chromosome 9q31, has eluded identification. We identified and characterized the RNAs encoded by this region of chromosome 9 in cell lines derived from individuals homozygous for the major FD haplotype, and we observed that the RNA encoding the IkappaB kinase complex-associated protein (IKAP) lacks exon 20 and, as a result of a frameshift, encodes a truncated protein. Sequence analysis reveals a T-->C transition in the donor splice site of intron 20. In individuals bearing a minor FD haplotype, a missense mutation in exon 19 disrupts a consensus serine/threonine kinase phosphorylation site. This mutation results in defective phosphorylation of IKAP. These mutations were observed to be present in a random sample of Ashkenazi Jewish individuals, at approximately the predicted carrier frequency of FD. These findings demonstrate that mutations in the gene encoding IKAP are responsible for FD.

Tay-Sachs screening in the Jewish Ashkenazi population: DNA testing is the preferred procedure

A unique screening program for the identification of Tay-Sachs Disease (TSD) heterozygotes has been performed in the tradi- tional Orthodox Ashkenazi Jewish (AJ) community since 1983. In recent years the program has utilized the biochemical assay for the determination of hexosaminidase A levels by the heat inactivation technique as well as by direct DNA analysis. The three mutations which were analyzed were those that have been shown to be prevalent among AJ TSD patients and carriers, namely the four nucleotide insertion mutation in exon 11 (1278+TATC), the splice mutation at the 5' end of intron 12 (1421+1g-->c), and the adult mutation, a Gly(269)-->Ser substitution in exon 5 (G269S). A total of 103,133 individuals were tested by biochemical analysis, and 38,197 of them were also assayed by DNA testing. Furthermore, 151 chromosomes from TSD patients or obligate heterozygotes were subjected to DNA analysis for one of the three mutations. DNA testing of the latter identified one of the three AJ mutations in every case, predicting a very high detection rate of heterozygotes in this community by this method. By contrast, the sensitivity of the enzyme assay ranged from 93.1% to 99.1% depending on the exclusion (inclusion) of inconclusive results as positive, while the specificity ranged from 88.1% to 98.8% depending on the inclusion (exclusion) of inconclusive results as positive. Our results strongly support the use of DNA testing alone as the most cost-effective and efficient approach to carrier screening for TSD in individuals of confirmed Ashkenazi Jewish ancestry.

Cystic fibrosis heterozygote screening in the Orthodox Community of Ashkenazi Jews: the Dor Yesharim approach and heterozygote frequency

In the community of the Orthodox Jews most of the marriages are arranged a screening program that is aimed at preventing the marriage of two carriers of autosomal recessive disorders is conducted by the Dor Yesharim organization. A random sample of 6,076 individuals of the Orthodox Jewish Ashkenazi community, were screened for the five mutations common in Ashkenazi patients (delta F508, W1282X, G542X, N1303K, 3849 + 10Kb C-->T). Two hundred thirty-two carriers were identified, giving a heterozygote frequency of 1:26. The relative frequencies of the individual mutations in the general population were comparable to those in the patients.

Chylous ascites as a presenting sign of prostatic adenocarcinoma

Chylous ascites is usually associated with either primary disorders of the lymphatic system or malignancies of the lymph nodes such as Hodgkin and non-Hodgkin lymphoma. We describe, however, a young man in whom chylous ascites was a presenting sign of disseminated adenocarcinoma of the prostate gland. Most likely retroperitoneal lymph nodal replacement and tumor blockade of lymphatic collectors by metastatic adenocarcinoma was responsible for the development of chylous ascites.