Objective: To identify the genetic defect causing autosomal dominant congenital cataract (ADCC) in a five-generation family in the northeast of China.
Methods: Linkage analysis was carried out with polymorphic microsatellites on the Human MapPairs marker set, special known loci. Mutation analysis of the candidate gene in the critical region was performed to detect the potential mutation.
Results: The maximum Lod score (2.44 at recombination fraction theta=0) was obtained for markers D1S498,D1S305, and D1S2844. The cataract locus in this family constellation was mapped to 1q21.1 and 21.44 cM interval between D1S2344 and D1S2844, which were known to flank the gene coding Connexin 50 (Cx50) or gap junction protein alpha-8 (GJA8). Sequencing of the coding region of GJA8 gene showed a heterozygous transversion T>G in exon 2, which resulted in the substitution of glycine for valine at amino acid 64, and this position was in the first connexin signature region that characterized this protein.
Conclusion: This is the first report on a mutation in the first connexin signature region of the GJA8 and a different mutation within Cx50 revealed in this family, which might account for the phenotypic differences observed. Furthermore, this study confirmed that GJA8 plays a vital role in the maintenance of human lens transparency.