A missense mutation in the human connexin50 gene (GJA8) underlies autosomal dominant "zonular pulverulent" cataract,on chromosome 1q.

CZP1, a locus for autosomal dominant "zonular pulverulent" cataract, previously had been linked with the Duffy blood-group-antigen locus on chromosome 1q. Here we report genetic refinement of the CZP1 locus and show that the underlying mutation is present in GJA8, the gene for connexin50. To map the CZP1 locus we performed linkage analysis using microsatellite markers on two distantly related branches of the original Ev. pedigree, which now spans eight generations. Significantly positive two-point LOD score (Z) values were obtained for markers D1S2669 (maximum Z [Zmax] = 4.52; maximum recombination frequency [thetamax] = 0) and D1S514 (Zmax = 4.48; thetamax = 0). Multipoint analysis gave Zmax = 5.22 (thetamax = 0) at marker D1S2669. Haplotyping indicated that CZP1 probably lies in the genetic interval D1S2746-(20.6 cM)-D1S2771. Sequence analysis of the entire protein-coding region of the GJA8 gene from the pedigree detected a C-->T transition in codon 88, which introduced a novel MnlI restriction-enzyme site that also cosegregated with the cataract. This missense mutation is predicted to result in the nonconservative substitution of serine for a phylogenetically conserved proline (P88S). These studies provide the first direct evidence that GJA8 plays a vital role in the maintenance of human lens transparency and identify the genetic defect believed to underlie the first inherited disease to be linked to a human autosome.     

A mutation in <Emphasis Type="Italic">ADIPOR1</Emphasis> causes nonsyndromic autosomal dominant retinitis pigmentosa

Retinitis pigmentosa (RP) is a clinically and genetically heterogeneous disorder characterized by night blindness, visual field constriction, and severely reduced visual acuity. Despite a number of genes being implicated in RP pathogenesis, the genetic etiology of the disease remains unknown in many patients. In this study, our aim was to identify the disease-causing mutation of a large Chinese family with autosomal dominant RP (adRP). Targeted exon capture sequencing was initially performed to screen mutations in known disease-causing genes, followed by exome sequencing. In doing so, a heterozygous mutation in ADIPOR1 (c.929A > G) that results in an amino acid substitution (p.Y310C) was identified to co-segregate with the disease phenotype in this family. Adipor1 is wildly expressed throughout the body, but appears to be enriched in the photoreceptor inner and outer segments. The p.Y310C mutation, predicted to affect the structure and function of the protein, was confirmed to affect protein folding and its subcellular localization in vitro. In addition, knockdown of adipor1 expression in a zebrafish model with morpholino (MO) preferentially reduced the number of rod photoreceptors, with no effect on the number of cones, a phenotype that is characteristic of RP. Furthermore, the knockdown phenotype was partially rescued by injecting wild-type, but not mutant, human ADIPOR1 mRNA. We conclude that ADIPOR1 is a novel adRP-causing gene and plays an important role in rod development and maintenance.     

Exome sequencing identifies novel and recurrent mutations in <Emphasis Type="Italic">GJA8</Emphasis> and <Emphasis Type="Italic">CRYGD</Emphasis>associated with inherited cataract

Background

Inherited cataract is a clinically important and genetically heterogeneous cause of visual impairment. Typically, it presents at an early age with or without other ocular/systemic signs and lacks clear phenotype-genotype correlation rendering both clinical classification and molecular diagnosis challenging. Here we have utilized trio-based whole exome sequencing to discover mutations in candidate genes underlying autosomal dominant cataract segregating in three nuclear families.

Results

In family A, we identified a recurrent heterozygous mutation in exon-2 of the gene encoding γD-crystallin (CRYGD; c.70C > A, p.Pro24Thr) that co-segregated with `coralliform' lens opacities. Families B and C were found to harbor different novel variants in exon-2 of the gene coding for gap-junction protein α8 (GJA8; c.20T > C, p.Leu7Pro and c.293A > C, p.His98Pro). Each novel variant co-segregated with disease and was predicted in silico to have damaging effects on protein function.

Conclusions

Exome sequencing facilitates concurrent mutation-profiling of the burgeoning list of candidate genes for inherited cataract, and the results can provide enhanced clinical diagnosis and genetic counseling for affected families.

     

Reconstruction of SNP haplotypes with mutation c.-23+1G&gt;A in human gene <Emphasis Type="Italic">GJB2</Emphasis> (Chromosome 13) in some populations of Eurasia

The c.-23+1G>A splice site mutation is one of the most frequent mutations of gene GJB2 (Cx26, 13q11-q12) associated with congenital non-syndromic autosomal recessive deafness. This mutation is characterized by a wide spread from Eastern Siberia and Central Asia to Eastern Europe, the Middle East, and South Asia. It is currently unknown whether this mutation spread over such a vast territory as a result of the founder effect or there were several local centers of origin of this mutation. For the first time, on the basis of the analysis of variability of nine SNP markers, five different haplotypes in deaf patients homozygous for mutation c.-23+1G>A from six Eurasian populations were reconstructed. The structure of the haplotypes revealed in Yakuts, Russians, Evenks, Tuvinians, Mongols, and Turks makes it possible to assume that mutation c.-23+1G>A (GJB2) could have spread across Eurasia as a result of the founder effect. The greatest diversity of haplotypes with c.-23+1G>A was found in patients from Mongolia, which probably refers to the earlier period of expansion of haplotypes carrying this mutation on the territory of Central Asia.     

Dense cataract and microphthalmia (<Emphasis Type="Italic">dcm</Emphasis>) in BALB/c mice is caused by mutations in the <Emphasis Type="Italic">GJA8</Emphasis> locus

A spontaneous mutation in BALB/c mice that causes congenital dense cataract and microphthalmia (dcm) was reported previously. This abnormality was found to be inheritable and the mode of inheritance indicated that this phenotype is due to mutation of an autosomal recessive gene. We performed genetic screen to identify the underlying mutations through linkage analysis with the dcm progenies of F₁ intercross. We identified the region of mutation on chromosome 3 and further mapping and sequence analysis identified the mutation in the GJA8 gene that encodes for connexin 50. The mutation represents a single nucleotide change at position 64 (G to C) that results in a change in the amino acid glycine to arginine at position 22 (G22R) and is identical to the mutation previously characterized as lop10. However, the phenotype of these mice differ from that of lop10 mice and since it is one of the very few genetic models with recessive pattern of inheritance, we propose that dcm mice can serve as a useful model for studying the dynamics and interaction of the gap junction formation in mouse eye development.     

Whole exome sequencing identified two novel homozygous missense variants in the same codon of <Emphasis Type="Italic">CLCN7</Emphasis> underlying autosomal recessive infantile malignant osteopetrosis in a Pakistani family

Autosomal recessive osteopetrosis is a severe fatal disorder with an average incidence of around 1:250,000. It is diagnosed soon after birth or within the 1st year of life with severe symptoms of abnormal bone remodelling. This study was aimed to identify the underlying genetic cause of the disease in a Pakistani family segregating infantile malignant osteopetrosis in autosomal recessive pattern. Whole exome sequencing of the proband was performed using the 51 Mb SureSelect V4 library kit and sequenced using the Illumina HiSeq2500 sequencing system. The reads were analysed using standard bioinformatic data analysis pipeline. The genotype of candidate variants was confirmed in the proband and his normal parents by Sanger sequencing. Two novel homozygous missense variants were found in the same codon 204 of CLCN7 NM_001287.5:c.[610A>T;612C>G] predicting p.(Ser204Trp) variant in the protein. Sanger sequencing and RFLP assay verified that both these variants were heterozygous in the unaffected parents. Moreover, these variants were not detected in the unrelated healthy Pakistani subjects (200 chromosomes), ExAC, dbSNP, or the 1000 Genomes Project data. Multiple bioinformatics tools unanimously predicted the p.(Ser204Trp) variant as deleterious. CLCN7 mutation p.(Ser204Trp) is the likely cause of the osteopetrosis disease in the Pakistani family. This study expands the restricted spectrum of CLCN7 mutations associated with infantile malignant osteopetrosis and indicates clinical significance of whole exome sequencing in the diagnosis of clinically and genetically heterogenous osteopetrosis phenotype. These data should be helpful in the improved genetic counselling, carrier identification and prenatal diagnosis of the affected family.     

Novel compound heterozygous mutations in the <Emphasis Type="Italic">GPR98</Emphasis> (<Emphasis Type="Italic">USH2C</Emphasis>) gene identified by whole exome sequencing in a Moroccan deaf family

In the present work, we identified two novel compound heterozygote mutations in the GPR98 (G protein-coupled receptor 98) gene causing Usher syndrome. Whole-exome sequencing was performed to study the genetic causes of Usher syndrome in a Moroccan family with three affected siblings. We identify two novel compound heterozygote mutations (c.1054C?>?A, c.16544delT) in the GPR98 gene in the three affected siblings carrying post-linguale bilateral moderate hearing loss with normal vestibular functions and before installing visual disturbances. This is the first time that mutations in the GPR98 gene are described in the Moroccan deaf patients.     

Whole-exome sequencing analysis reveals co-segregation of a <Emphasis Type="Italic">COL20A1</Emphasis> missense mutation in a Pakistani family with striate palmoplantar keratoderma

Palmoplantar keratoderma (PPK) is a rare group of excessive skin disorder characterized by thickness over the palms and soles. The striate palmoplantar keratoderma (PPKS) is a form in which hyperkeratotic lesions are restricted to the pressure regions extending longitudinally in the length of each finger to the palm. Dominantly inherited mutations in genes including desmoglein 1, desmoplakin and keratin 1 have been suggested as genetic causes of PPKS. In this study, we investigated a three-generation Pakistani family segregating PPKS phenotype in autosomal dominant fashion to identify genetic cause in this family. We have performed whole-exome and Sanger sequencing followed by in silico bioinformatics analysis to pinpoint candidate mutation associated with PPK. Revealed a novel heterozygous mutation (NM_020882.2, COL20A1 c. 392C?>?G; p.Ser131Cys) in the loop region close to fibronectin type III-1 domain of the c ollagen 20 α1. This variant was not found in our in-house 219 ethnically matched Pakistani unaffected controls and showed minor allele frequency of 3.4 × 10^?5 in Exome Aggregation Consortium database containing exome data of 59,464 worldwide individuals. It was assigned as “pathogenic” by in silico prediction tools. Previously, association of mutation in the COL14A1, one of the paralogous gene of COL20A1, with PPK was reported in the study with a Chinese family. Our study proposes COL20A1 gene as another potential candidate gene for PPKS which expand the spectrum of collagen proteins in the pathogenicity of PPK.