A novel GJA8 mutation (p.I31T) causing autosomal dominant congenital cataract in a Chinese family

Abstract

Purpose: To identify the genetic defect associated with autosomal dominant congenital nuclear cataract in a Chinese family.

Methods: Family history and clinical data were recorded. The genomic DNA was extracted from peripheral blood leukocytes. All the members were genotyped with microsatellite markers at loci considered to be associated with cataracts. Two-point logarithm of odds (LOD) scores were calculated by using the Linkage software after genotyping. Mutations were detected by DNA sequence analysis of the candidate genes. Effects of amino acid changes on the structure and function of proteins were predicted by bioinformatics analysis.

Results: Evidence of a linkage was obtained at markers D1S514 (LOD score [Z]=3.48, recombination fraction [theta]=0.0) and D1S1595 (Z=2.49, theta=0.0). Haplotype analysis indicated that the cataract gene was close to these two markers. Sequencing of the connexin 50 (GJA8) gene revealed a T>C transition at nucleotide position c.92. This nucleotide change resulted in the substitution of highly conserved isoleucine by threonine at codon 31(I31T). This mutation co-segregated with all affected individuals and was not observed in unaffected or 110 normal unrelated individuals. Bioinformatics analysis showed that a highly conserved region was located at Ile31, and the mutation was predicted to affect the function and secondary structure of the GJA8 protein.

Conclusion: A novel mutation in GJA8 was detected in a Chinese family with autosomal dominant congenital nuclear cataract, providing clear evidence of a relationship between the genotype and the corresponding cataract phenotype.

Figure 1

Slit lamp photographs of the proband. The photograph of the proband (V:3) shows that the opacity is a nuclear cataract. Both the fetal nucleus and the embryonic nucleus display white opacities.

Figure 2

Cataract pedigree and haplotype analysis. Pedigree and haplotype analysis of the cataract family shows the segregation of two microsatellite markers on chromosome 1p12-q22. Squares and circles indicate males and females, respectively. Blackened symbols and bars denote affected status.

Figure 3

DNA sequence chromatograms. DNA sequence chromatograms of the unaffected members and affected members in an autosomal dominant nuclear cataract family. A single transition is observed at position 92 (T>C) as a T/C double peak (indicated by an arrow).

Figure 4

The predicted secondary structures of the mutant and the wild-type amino acid sequences. The predicted secondary structures of the wild-type amino acid sequence (A) and the mutant amino acid sequence (B) is shown. The target sequences are labeled by a red circle, which indicate that there is a helix in the wild type replaced by a turn in the mutant type. Blue, helix; yellow, sheet; green, turn; black, coin.

Figure 5

Multiple-sequence alignment in GJA8 from different species. A multiple alignment of partial amino acid sequences of GJA8 from different species is shown. The alignment data indicate that isoleucine at position 31 (indicated by an arrow) is highly conserved in different species in GJA8.