Transmission ratio distortion of mutations in the master regulator of centriole biogenesis PLK4.

The evolutionary conserved Polo-like kinase 4 (PLK4) is essential for centriole duplication, spindle assembly, and de novo centriole formation. In man, homozygous mutations in PLK4 lead to primary microcephaly, altered PLK4 expression is associated with aneuploidy in human embryos. Here, we report on a consanguineous four-generation family with 8 affected individuals compound heterozygous for a novel missense variant, c.881 T > G, and a deletion of the PLK4 gene. The clinical phenotype of the adult patients is mild compared to individuals with previously described PLK4 mutations. One individual was homozygous for the variant c.881G and phenotypically unaffected. The deletion was inherited by 14 of 16 offspring and thus exhibits transmission ratio distortion (TRD). Moreover, based on the already published families with PLK4 mutations, it could be shown that due to the preferential transmission of the mutant alleles, the number of affected offspring is significantly increased. It is assumed that reduced expression of PLK4 decreases the intrinsically high error rate of the first cell divisions after fertilization, increases the number of viable embryos and thus leads to preferential transmission of the deleted/mutated alleles.

Directed Alternative Splicing in Nijmegen Breakage Syndrome: Proof of Principle Concerning Its Therapeutical Application.

Over 90% of patients with Nijmegen breakage syndrome (NBS), a hereditary cancer disorder, are homoallelic for a 5 bp deletion in the NBN gene involved in the cellular response to DNA damage. This hypomorphic mutation leads to a carboxy-terminal protein fragment, p70-nibrin, with some residual function. Average age at malignancy, typically lymphoma, is 9.7 years. NBS patients are hypersensitive to chemotherapeutic and radiotherapeutic treatments, thus prevention of cancer development is of particular importance. Expression of an internally deleted NBN protein, p80-nibrin, has been previously shown to be associated with a milder cellular phenotype and absence of cancer in a 62-year-old NBS patient. Here we show that cells from this patient, unlike other NBS patients, have DNA replication and origin firing rates comparable to control cells. We used here antisense oligonucleotides to enforce alternative splicing in NBS patient cells and efficiently generate the same internally deleted p80-nibrin protein. Injecting the same antisense sequences as morpholino oligomers (VivoMorpholinos) into the tail vein of a humanized NBS murine mouse model also led to efficient alternative splicing in vivo. Thus, proof of principle for the use of antisense oligonucleotides as a potential cancer prophylaxis has been demonstrated.

5-Methylcytosine-Rich Heterochromatin in the Indian Muntjac.

Two 5-methylcytosine (5-MeC)-rich heterochromatic regions were demonstrated in metaphase chromosomes of the Indian muntjac by indirect immunofluorescence using a monoclonal anti-5-MeC antibody. The metaphases were obtained from diploid and triploid cell lines. A major region is located in the 'neck' of the 3;X fusion chromosome and can be detected after denaturation of the chromosomal DNA with UV-light irradiation for 1 h. It is located exactly at the border of the X chromosome and the translocated autosome 3. A minor region is found in the centromeric region of the free autosome 3 after denaturing the chromosomal DNA for 3 h or longer. The structure and possible function of the major hypermethylated region as barrier against spreading of the X-inactivation process into the autosome 3 is discussed.

Evidence for an increase in trisomy 21 (Down syndrome) in Europe after the Chernobyl reactor accident.

The objective of this study is to investigate the prevalence of Down syndrome (DS) associated with Chernobyl fallout. Maternal age-adjusted DS data and corresponding live birth data from the following seven European countries or regions were analyzed: Bavaria and West Berlin in Germany, Belarus, Hungary, the Lothian Region of Scotland, North West England, and Sweden from 1981 to 1992. To assess the underlying time trends in the DS occurrence, and to investigate whether there have been significant changes in the trend functions after Chernobyl, we applied logistic regression allowing for peaks and jumps from January 1987 onward. The majority of the trisomy 21 cases of the previously reported, highly significant January 1987 clusters in Belarus and West Berlin were conceived when the radioactive clouds with significant amounts of radionuclides with short physical half-lives, especially (131)iodine, passed over these regions. Apart from this, we also observed a significant longer lasting effect in both areas. Moreover, evidence for long-term changes in the DS prevalence in several other European regions is presented and explained by exposure, especially to (137)Cs. In many areas, (137)Cs uptake reached its maximum one year after the Chernobyl accident. Thus, the highest increase in trisomy 21 should be observed in 1987/1988, which is indeed the case. Based on the fact that maternal meiosis is an error prone process, the assumption of a causal relationship between low-dose irradiation and nondisjunction is the most likely explanation for the observed increase in DS after the Chernobyl reactor accident.

Identification of a novel candidate gene for non-syndromic autosomal recessive intellectual disability: the WASH complex member SWIP.

High-throughput sequencing has greatly facilitated the elucidation of genetic disorders, but compared with X-linked and autosomal dominant diseases, the search for genetic defects underlying autosomal recessive diseases still lags behind. In a large consanguineous family with autosomal recessive intellectual disability (ARID), we have combined homozygosity mapping, targeted exon enrichment and high-throughput sequencing to identify the underlying gene defect. After appropriate single-nucleotide polymorphism filtering, only two molecular changes remained, including a non-synonymous sequence change in the SWIP [Strumpellin and WASH (Wiskott-Aldrich syndrome protein and scar homolog)-interacting protein] gene, a member of the recently discovered WASH complex, which is involved in actin polymerization and multiple endosomal transport processes. Based on high pathogenicity and evolutionary conservation scores as well as functional considerations, this gene defect was considered as causative for ID in this family. In line with this assumption, we could show that this mutation leads to significantly reduced SWIP levels and to destabilization of the entire WASH complex. Thus, our findings suggest that SWIP is a novel gene for ARID.

Mutations in the gene encoding the lamin B receptor produce an altered nuclear morphology in granulocytes (Pelger-Huët anomaly).

Pelger-Huët anomaly (PHA; OMIM *169400) is an autosomal dominant disorder characterized by abnormal nuclear shape and chromatin organization in blood granulocytes. Affected individuals show hypolobulated neutrophil nuclei with coarse chromatin. Presumed homozygous individuals have ovoid neutrophil nuclei, as well as varying degrees of developmental delay, epilepsy and skeletal abnormalities. Homozygous offspring in an extinct rabbit lineage showed severe chondrodystrophy, developmental anomalies and increased pre- and postnatal mortality. Here we show, by carrying out a genome-wide linkage scan, that PHA is linked to chromosome 1q41-43. We identified four splice-site, two frameshift and two nonsense mutations in LBR, encoding the lamin B receptor. The lamin B receptor (LBR), a member of the sterol reductase family, is evolutionarily conserved and integral to the inner nuclear membrane; it targets heterochromatin and lamins to the nuclear membrane. Lymphoblastoid cells from heterozygous individuals affected with PHA show reduced expression of the lamin B receptor, and cells homozygous with respect to PHA contain only trace amounts of it. We found that expression of the lamin B receptor affects neutrophil nuclear shape and chromatin distribution in a dose-dependent manner. Our findings have implications for understanding nuclear envelope-heterochromatin interactions, the pathogenesis of Pelger-like conditions in leukemia, infection and toxic drug reactions, and the evolution of neutrophil nuclear shape.

Population monitoring of trisomy 21: problems and approaches.

Trisomy 21 (Down syndrome) is the most common autosomal aneuploidy among newborns. About 90% result from meiotic nondisjunction during oogenesis, which occurs around conception, when also the most profound epigenetic modifications take place. Thus, maternal meiosis is an error prone process with an extreme sensitivity to endogenous factors, as exemplified by maternal age. This contrasts with the missing acceptance of causal exogenous factors. The proof of an environmental agent is a great challenge, both with respect to ascertainment bias, determination of time and dosage of exposure, as well as registration of the relevant individual health data affecting the birth prevalence. Based on a few exemplary epidemiological studies the feasibility of trisomy 21 monitoring is illustrated. In the nearer future the methodical premises will be clearly improved, both due to the establishment of electronic health registers and to the introduction of non-invasive prenatal tests. Down syndrome is a sentinel phenotype, presumably also with regard to other congenital anomalies. Thus, monitoring of trisomy 21 offers new chances for risk avoidance and preventive measures, but also for basic research concerning identification of relevant genomic variants involved in chromosomal nondisjunction.

The NBN founder mutation-Evidence for a country specific difference in age at cancer manifestation.

BACKGROUND: Nijmegen breakage syndrome (NBS) is an autosomal-recessive chromosome instability disorder characterized by, among others, hypersensitivity to X-irradiation and an exceptionally high risk for lymphoid malignancy. The vast majority of NBS patients is homozygous for a common Slavic founder mutation, c.657del5, of the NBN gene, which is involved in the repair of DNA double-strand breaks (DSBs). The founder mutation also predisposes heterozygous carriers to cancer, apparently however, with a higher risk in the Czech Republic/Slovakia (CS) than in Poland. AIM: To examine whether the age of cancer manifestation and cancer death of NBN homozygotes is different between probands from CS and Poland. METHODS: The study is restricted to probands born until 1989, before replacement of the communist regime by a democratic system in CS and Poland, and a substantial transition of the health care systems. Moreover, all patients were recruited without knowledge of their genetic status since the NBN gene was not identified until 1998. RESULTS: Here, we show that cancer manifestation of NBN homozygotes is at a significantly earlier age in probands from CS than from Poland. This is explained by the difference in natural and medical radiation exposure, though within the permissible dosage. CONCLUSION: It is reasonable to assume that this finding also sheds light on the higher cancer risk of NBN heterozygotes in CS than in Poland. This has implications for genetic counseling and individualized medicine also of probands with other DNA repair defects.

New mutations in the ATM gene and clinical data of 25 AT patients.

Ataxia telangiectasia (AT) is an autosomal recessive disorder characterized by cerebellar degeneration, immunodeficiency, oculocutaneous telangiectasias, chromosomal instability, radiosensitivity, and cancer predisposition. The gene mutated in the patients, ATM, encodes a member of the phosphatidylinositol 3-kinase family proteins. The ATM protein has a key role in the cellular response to DNA damage. Truncating and splice site mutations in ATM have been found in most patients with the classical AT phenotype. Here we report of our extensive ATM mutation screening on 25 AT patients from 19 families of different ethnic origin. Previously unknown mutations were identified in six patients including a new homozygous missense mutation, c.8110T>C (p.Cys2704Arg), in a severely affected patient. Comprehensive clinical data are presented for all patients described here along with data on ATM function generated by analysis of cell lines established from a subset of the patients.

Assisted reproductive technologies do not enhance the variability of DNA methylation imprints in human.

BACKGROUND Assisted reproductive technologies (ART) such as in vitro fertilisation (IVF) and intracytoplasmic sperm injection (ICSI) are believed to destabilise genomic imprints. An increased frequency of Beckwith-Wiedemann syndrome in children born after ART has been reported. Other, mostly epidemiological, studies argue against this finding. OBJECTIVE To examine the effect of ART on the stability of DNA methylation imprints, DNA was extracted from maternal peripheral blood (MPB), umbilical cord blood (UCB) and amnion/chorion tissue (ACT) of 185 phenotypically normal children (77 ICSI, 35 IVF, and 73 spontaneous conceptions). Using bisulfite based technologies 10 differentially methylated regions (DMRs) were analysed, including KvDMR1, H19, SNRPN, MEST, GRB10, DLK1/MEG3 IG-DMR, GNAS NESP55, GNAS NESPas, GNAS XL-alpha-s and GNAS Exon1A. RESULTS Methylation indices (MI) do not reveal any significant differences at nine DMRs among the conception groups in neither MPB, UCB nor in ACT. The only slightly variable DMR was that of MEST. Here the mean MI was higher in UCB and MPB of IVF cases (mean MI+/-SD: 0.41+/-0.03 (UCB) and 0.40+/-0.03 (MPB)) compared to the ICSI (0.38+/-0.03, p=0.003 (UCB); 0.37+/-0.04, p=0.0007 (MPB)) or spontaneous cases (0.38+/-0.03, p=0.003 (UCB); 0.38+/-0.04, p=0.02 (MPB)). Weak but suggestive correlations between DMRs were, however, found between MPB, UCB and ACT. CONCLUSION This study supports the notion that children conceived by ART do not show a higher degree of imprint variability and hence do not have an a priori higher risk for imprinting disorders.

Clinical variability and novel mutations in the NHEJ1 gene in patients with a Nijmegen breakage syndrome-like phenotype.

We have previously shown that mutations in the genes encoding DNA Ligase IV (LIGIV) and RAD50, involved in DNA repair by nonhomologous-end joining (NHEJ) and homologous recombination, respectively, lead to clinical and cellular features similar to those of Nijmegen Breakage Syndrome (NBS). Very recently, a new member of the NHEJ repair pathway, NHEJ1, was discovered, and mutations in patients with features resembling NBS were described. Here we report on five patients from four families of different ethnic origin with the NBS-like phenotype. Sequence analysis of the NHEJ1 gene in a patient of Spanish and in a patient of Turkish origin identified homozygous, previously reported mutations, c.168C>G (p.Arg57Gly) and c.532C>T (p.Arg178Ter), respectively. Two novel, paternally inherited truncating mutations, c.495dupA (p.Asp166ArgfsTer20) and c.526C>T (p.Arg176Ter) and two novel, maternal genomic deletions of 1.9 and 6.9 kb of the NHEJ1 gene, were found in a compound heterozygous state in two siblings of German origin and in one Malaysian patient, respectively. Our findings confirm that patients with NBS-like phenotypes may have mutations in the NHEJ1 gene including multiexon deletions, and show that considerable clinical variability could be observed even within the same family.

Telomere attrition and dysfunction: a potential trigger of the progeroid phenotype in nijmegen breakage syndrome.

BACKGROUND: Nibrin, as part of the NBN/MRE11/RAD50 complex, is mutated in Nijmegen breakage syndrome (NBS), which leads to impaired DNA damage response and lymphoid malignancy. RESULTS: Telomere length (TL) was markedly reduced in homozygous patients (and comparably so in all chromosomes) by ~40% (qPCR) and was slightly reduced in NBS heterozygotes older than 30 years (~25% in qPCR), in accordance with the respective cancer rates. Humanized cancer-free NBS mice had normal TL. Telomere elongation was inducible by telomerase and/or alternative telomere lengthening but was associated with abnormal expression of telomeric genes involved in aging and/or cell growth. Lymphoblastoid cells from NBS patients with long survival times (>12 years) displayed the shortest telomeres and low caspase 7 activity. CONCLUSIONS: NBS is a secondary telomeropathy. The two-edged sword of telomere attrition enhances the cancer-prone situation in NBS but can also lead to a relatively stable cellular phenotype in tumor survivors. Results suggest a modular model for progeroid syndromes with abnormal expression of telomeric genes as a molecular basis. METHODS: We studied TL and function in 38 homozygous individuals, 27 heterozygotes, one homozygous fetus, six NBS lymphoblastoid cell lines, and humanized NBS mice, all with the same founder NBN mutation: c.657_661del5.

Novel mutation in the gamma-S crystallin gene causing autosomal dominant cataract.

PURPOSE: To identify the underlying genetic defect in a north Indian family with seven members in three-generations affected with bilateral congenital cataract. METHODS: Detailed family history and clinical data were recorded. Linkage analysis using fluorescently labeled microsatellite markers for the already known candidate gene loci was performed in combination with mutation screening by bidirectional sequencing. RESULTS: Affected individuals had bilateral congenital cataract. Cataract was of opalescent type with the central nuclear region denser than the periphery. Linkage was excluded for the known cataract candidate gene loci at 1p34-36, 1q21-25 (gap junction protein, alpha 8 [GJA8]), 2q33-36 (crystallin, gamma A [CRYGA], crystallin, gamma B [CRYGB], crystallin, gamma C [CRYGC], crystallin, gamma D [CRYGD], crystallin, beta A2 [CRYBA2]), 3q21-22 (beaded filament structural protein 2, phakinin [BFSP2]), 12q12-14 (aquaporin 0 [AQP0]), 13q11-13 (gap junction protein, alpha 3 [GJA3]), 15q21-22, 16q22-23 (v-maf musculoaponeurotic fibrosarcoma oncogene homolog [MAF], heat shock transcription factor 4 [HSF4]), 17q11-12 (crystallin, beta A1 [CRYBA1]), 17q24, 21q22.3 (crystallin, alpha A [CRYAA]), and 22q11.2 (crystallin, beta B1 [CRYBB1], crystallin, beta B2 [CRYBB2], crystallin, beta B3 [CRYBB3], crystallin, beta A4 [CRYBA4]). Crystallin, alpha B (CRYAB) at chromosome 11q23-24 was excluded by sequence analysis. However, sequencing the candidate gene, crystallin, gamma S (CRYGS), at chromosome 3q26.3-qter showed a heterozygous c.176G-->A change that resulted in the replacement of a structurally highly conserved valine by methionine at codon 42 (p.V42M). This sequence change was not observed in unaffected family members or in the 100 ethnically matched controls. CONCLUSIONS: We report a novel missense mutation, p.V42M, in CRYGS associated with bilateral congenital cataract in a family of Indian origin. This is the third report of a mutation in this exceptional member of the beta-/gamma-crystallin superfamily and further substantiates the genetic and clinical heterogeneity of autosomal dominant cataract.

Extreme variation in apoptosis capacity amongst lymphoid cells of Nijmegen breakage syndrome patients.

The human genetic disorder, Nijmegen breakage syndrome (NBS), is characterised by radiosensitivity, immunodeficiency and an increased risk for cancer, particularly lymphoma. The NBS1 gene codes for a protein, nibrin, involved in the processing/repair of DNA double strand breaks and in cell cycle checkpoints. The majority of patients (>90%) are homozygous for a founder mutation. Despite this genetic homogeneity, the syndrome shows considerable clinical variability, for example, in age at development of a malignancy. We hypothesised that one reason for such variation might be individual differences in the clearance of heavily damaged precancerous cells by apoptosis. To test this hypothesis we have examined a set of 30 lymphoblastoid B-cell lines from NBS patients for their capacity to enter into apoptosis after a DNA-damaging treatment. There was a substantial 40-fold variation in apoptosis between cell lines from different patients. NBS patient cell lines could be grouped into a large, apoptosis-deficient group and a smaller group with essentially normal apoptotic response to DNA damage. In both groups, cell lines were proficient in TP53 phosphorylation and stabilisation after the same DNA-damaging treatment. Thus the observed variation in apoptosis capacity is not due to failure to activate TP53. Despite the large variation in apoptosis, no statistically significant correlation between apoptotic capacity of patient cell lines and clinical course of the disease was apparent.

A mutation in GJA8 (p.P88Q) is associated with "balloon-like" cataract with Y-sutural opacities in a family of Indian origin.

PURPOSE: To detect the underlying genetic defect in a family with three members in two generations affected with bilateral congenital cataract. METHODS: Detailed family history and clinical data were recorded. Mutation screening in the candidate genes, alphaA-crystallin (CRYAA), betaA1-crystallin (CRYBA1), betaB2-crystallin (CRYBB2), gammaA-gammaD-crystallins (CRYGA, CRYGB, CRYGC, and CRYGD), connexin-46 (GJA3), and connexin-50 (GJA8), was performed by bidirectional sequencing of the amplified products. RESULTS: Affected individuals had "balloon-like" cataract with prominent Y-sutural opacities. Sequencing of the candidate genes showed a heterozygous c.262C>A change in the gene for connexin 50 (GJA8), which is localized at 1q21, that resulted in the replacement of a highly conserved proline by glutamine (p.P88Q). This sequence change was not observed in 96 ethnically matched controls. CONCLUSIONS: We report a p.P88Q mutation in GJA8 associated with Y-sutural cataract in a family of Indian origin. Mutations of the same codon have previously been described in British families with pulverulent cataract, suggesting that modifying factors may determine the type of cataract.

A novel mutation in GJA8 associated with jellyfish-like cataract in a family of Indian origin.

PURPOSE: To identify the underlying genetic defect in a three-generation family with five members affected with dominant bilateral congenital cataract and microcornea. METHODS: Detailed family history and clinical data were recorded. Mutation screening in the candidate genes, CRYAA, CRYBB1, MAF, GJA3, and GJA8, was performed by bidirectional sequencing of the amplified products. RESULTS: Affected individuals had a jellyfish-like cataract in association with microcornea. Sequencing of GJA8 (connexin 50) showed a novel, heterozygous c.134G-->C change that resulted in the substitution of a highly conserved tryptophan by serine (p.W45S). This sequence change segregated completely with the disease phenotype and was not observed in 108 ethnically matched controls (216 chromosomes). However, an identical substitution has previously been described in GJA3 (connexin 46) leading to autosomal dominant nuclear cataract without microcornea. CONCLUSIONS: This is a novel mutation identified in the first transmembrane domain (M1) of GJA8. These findings further expand the mutation spectrum of connexin 50 (Cx50) in association with congenital cataract and microcornea.

Yeast XRS2 and human NBN gene: Experimental evidence for homology using codon optimized cDNA.

The genes, XRS2 in Saccharomyces cerevisiae and NBN in mammals, have little sequence identity at the amino acid level. Nevertheless, they are both found together with MRE11 and RAD50 in a highly conserved protein complex which functions in the repair of DNA double-strand breaks. Here, we have examined the evolutionary and functional relationship of these two genes by cross-complementation experiments. These experiments necessitated sequence correction for specific codon usage before they could be successfully conducted. We present evidence that despite extreme sequence divergence nibrin can, at least partially, replace Xrs2 in the cellular DNA damage response, and Xrs2 is able to promote nuclear localization of MRE11 in NBS cells. We discuss that the extreme sequence divergence reflects a unique adaptive pressure during evolution related to the specific eukaryotic role for both Xrs2 and nibrin in the subcellular localisation of the DNA repair complex. This, we suggest, is of particular relevance when cells are infected by viruses. The conflict hypothesis of co-evolution of DNA repair genes and DNA viruses may thus explain the very low sequence identity of these two homologous genes.

Evidence for a pre-malignant cell line in a skin biopsy from a patient with Nijmegen breakage syndrome.

BACKGROUND: Nijmegen breakage syndrome is an autosomal recessive disorder characterized by microcephaly, immunodeficiency, hypersensitivity to X-irradiation, and a high predisposition to cancer. Nibrin, the product of the NBN gene, is part of the MRE11/RAD50 (MRN) complex that is involved in the repair of DNA double strand breaks (DSBs), and plays a critical role in the processing of DSBs in immune gene rearrangements, telomere maintenance, and meiotic recombination. NBS skin fibroblasts grow slowly in culture and enter early into senescence. CASE PRESENTATION: Here we present an incidental finding. Skin fibroblasts, derived from a 9 year old NBS patient, showed a mosaic of normal diploid cells (46,XY) and those with a complex, unbalanced translocation. The aberrant karyotype was analysed by G-banding, comparative genomic hybridization, and whole chromosome painting. The exact breakpoints of the derivative chromosome were mapped by whole genome sequencing: 45,XY,der(6)(6pter → 6q11.1::13q11 → 13q21.33::20q11.22 → 20qter),-13. The deleted region of chromosomes 6 harbors almost 1.400 and that of chromosome 13 more than 500 genes, the duplicated region of chromosome 20 contains about 700 genes. Such unbalanced translocations are regularly incompatible with cellular survival, except in malignant cells. The aberrant cells, however, showed a high proliferation potential and could even be clonally expanded. Telomere length was significantly reduced, hTERT was not expressed. The cells underwent about 50 population doublings until they entered into senescence. The chromosomal preparation performed shortly before senescence showed telomere fusions, premature centromere divisions, endoreduplications and tetraploid cells, isochromatid breaks and a variety of marker chromosomes. Inspection of the site of skin biopsy 18 years later, presented no evidence for abnormal growth. CONCLUSIONS: The aberrant cells had a significant selective advantage in vitro. It is therefore tempting to speculate that this highly unbalanced translocation could be a primary driver of cancer cell growth.

Multisite de novo mutations in human offspring after paternal exposure to ionizing radiation.

A genome-wide evaluation of the effects of ionizing radiation on mutation induction in the mouse germline has identified multisite de novo mutations (MSDNs) as marker for previous exposure. Here we present the results of a small pilot study of whole genome sequencing in offspring of soldiers who served in radar units on weapon systems that were emitting high-frequency radiation. We found cases of exceptionally high MSDN rates as well as an increased mean in our cohort: While a MSDN mutation is detected in average in 1 out of 5 offspring of unexposed controls, we observed 12 MSDNs in altogether 18 offspring, including a family with 6 MSDNs in 3 offspring. Moreover, we found two translocations, also resulting from neighboring mutations. Our findings indicate that MSDNs might be suited in principle for the assessment of DNA damage from ionizing radiation also in humans. However, as exact person-related dose values in risk groups are usually not available, the interpretation of MSDNs in single families would benefit from larger molecular epidemiologic studies on this new biomarker.

A novel mutation in the connexin 46 (GJA3) gene associated with autosomal dominant congenital cataract in an Indian family.

PURPOSE: To identify the genetic defect in an autosomal dominant congenital cataract family (ADCC), having 18 individuals in four generations affected with embryonal cataract. METHODS: A genome wide scan using the GeneChip Human Mapping 10K Array, version 2 was performed on DNA samples from eight affected and two unaffected members of an ADCC family having 18 members in four generations affected with embryonal cataract. The region of potential linkage delimited by single nucleotide polymorphic (SNP) markers was analyzed using fluorescently labeled microsatellite markers. Mutation screening was performed in the candidate gene by bidirectional sequencing of amplified products. RESULTS: By whole genome screening linkage in this family, the genetic defect was located to a region of chromosome 13q11 which contains the candidate gene connexin 46 (GJA3) for ADCC. Sequencing of the coding region of GJA3 showed a novel heterozygous 98G>T change resulting in the substitution of highly conserved arginine by leucine at codon 33 (R33L), located in the first transmembrane domain of GJA3. This nucleotide change was not seen in any unaffected members of this family nor in 50 unrelated control subjects. CONCLUSIONS: The present study describes a novel mutation (R33L) in the GJA3 associated with finely granular embryonal cataract. These findings expand the mutation spectrum of GJA3 in association with congenital cataract.