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.

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 deleterious mutation in the PEX2 gene causes Zellweger syndrome in individuals of Ashkenazi Jewish descent.

Zellweger syndrome is known to be caused by numerous mutations that occur in at least 12 of the PEX genes. While phenotypes vary, many are severely debilitating, and death can result in affected newborns. Since the disease follows an autosomal recessive pattern of inheritance, carrier screening can be done for at-risk couples, but the number of potential mutations sites to screen can be daunting. Ethnicity-specific studies can help narrow this range by highlighting mutations that are present at higher percentages in certain populations. In this article, the carrier frequencies for two mutations causative of the severe Zellweger syndrome spectrum phenotype that occur in the PEX2 gene, c.355C>T and c.550del, were studied in individuals of Ashkenazi Jewish descent in order to advise on inclusion in existing carrier screening mutation panels for this population. The screening was performed for 2093 individuals through the use of TaqMan genotyping assays, real-time PCR, and allelic discrimination. Results indicated a carrier frequency of 0.813% (±0.385%) for the c.355C>T mutation and a carrier frequency of 0.00% (±0.00%) for the c.550del mutation. On the basis of these frequencies, we believe that the c.355C>T mutation should be considered for inclusion in carrier screening panels for the Ashkenazi population.

Carrier frequency of two BBS2 mutations in the Ashkenazi population.

Bardet-Biedl syndrome (BBS) is known to be caused by numerous mutations that occur in at least 15 of the BBS genes. As the disease follows an autosomal recessive pattern of inheritance, carrier screening can be performed for at-risk couples, but the number of potential mutation sites to screen can be daunting. Ethnic studies can help to narrow this range by highlighting mutations that are present at higher percentages in certain populations. In this article, the carrier frequency for two mutations that occur in the BBS2 gene, c.311A>C and c.1895G>C were studied in individuals of Ashkenazi Jewish descent in order to advise on including them in existing mutation panels for this population. Carrier screenings were performed on individuals from the Ashkenazi Jewish population using a combination of TaqMan genotyping assays followed by real-time polymerase chain reaction (PCR) and allelic discrimination, and allele-specific PCR confirmed by restriction analysis. The combined results indicated carrier frequencies of 0.473% (±0.0071%) for the c.311A>C mutation and 0.261% (±0.0064%) for the c.1895G>C mutation. On the basis of these frequencies, we believe that the two mutations should be considered for inclusion in screening panels for the Ashkenazi population.

A founder mutation in COL4A3 causes autosomal recessive Alport syndrome in the Ashkenazi Jewish population.

Alport syndrome is an inherited progressive nephropathy arising from mutations in the type IV collagen genes, COL4A3, COL4A4, and COL4A5. Symptoms also include sensorineural hearing loss and ocular lesions. We determined the molecular basis of Alport syndrome in a non-consanguineous Ashkenazi Jewish family with multiple affected females using linkage analysis and next generation sequencing. We identified a homozygous COL4A3 mutation, c.40_63del, in affected individuals with mutant alleles inherited from each parent on partially conserved haplotypes. Large-scale population screening of 2017 unrelated Ashkenazi Jewish samples revealed a carrier frequency of 1 in 183 indicating that COL4A3 c.40_63del is a founder mutation which may be a common cause of Alport syndrome in this population. Additionally, we determined that heterozygous mutation carriers in this family do not meet criteria for a diagnosis of Thin Basement Membrane Nephropathy and concluded that carriers of c.40_63del are not likely to develop benign familial hematuria.