Purpose: To screen for pathogenic mutations in ten candidate genes in Indian families diagnosed with autosomal recessive and autosomal dominant cataracts.
Methods: Families with two or more affected individuals with bilateral familial congenital/developmental cataract were ophthalmically evaluated, and blood samples were obtained. Genomic DNA extracted from the blood leukocytes was screened with PCR amplification of the exons and the flanking intronic regions of various genes selected for analysis. The amplified products were subjected to single strand conformation polymorphism (SSCP) analysis. The variants in SSCP analysis were subjected to bidirectional sequencing by automated methods.
Results: We identified four novel sequence changes that cosegregated with the disease phenotype in each family and were absent in at least 50 ethnically matched unrelated normal controls. These changes include a homozygous missense change of c.649G>A (Val196Met) in GJA8/connexin 50 (Cx50) in a family with autosomal recessive cataract, two heterozygous missense changes, c.658C>T (Pro199Ser) in GJA8/Cx50 and c.589C>T (Pro197Ser) in GJA3/connexin 46 (Cx46) in two separate families with autosomal dominant cataract, and a silent change ( c.84G>A/p.Val28Val, predicted to result in the creation of a new potential branch point) in GJA8 one family with an autosomal dominant inheritance of cataract. Of the four novel mutations identified, three mutations, Val196Met (GJA8), Pro199Ser (GJA8), and Pro197Ser (GJA3), are predicted to be in the second extracellular domain of the respective connexin proteins.
Conclusions: Our report extends the mutation spectrum of connexin genes GJA8 and GJA3 and confirms that connexin genes are among the most frequently mutated genes in hereditary cataracts. Our results suggest that connexin gene (GJA8 and GJA3) mutations occur in approximately 10% (4/40 families) of families with congenital hereditary cataracts in a population from southern India.