Connexin46 mutations in autosomal dominant congenital cataract

Loci for autosomal dominant "zonular pulverulent" cataract have been mapped to chromosomes 1q(CZP1) and 13q (CZP3). Here we report genetic refinement of the CZP3 locus and identify underlying mutations in the gene for gap-jun ction protein alpha-3 (GJA3), or connexin46 (Cx46). Linkage analysis gave a significantly positive two-point LOD score (Z) at marker D13S175 (maximum Z [Z(max)] = > 7.0; maximum recombination frequency [theta(max)] = 0). Hapl otyping indicated that CZP3 probably lies in the genetic interval D1381236- D13S175-D13S1316-cen-13pter, close to GJA3. Sequencing of a genomic clone i solated from the CZP3 candidate region identified an open reading frame cod ing for a protein of 435 amino acids (47,435 D) that shared similar to 88% homology with rat Cx46. Mutation analysis of GJA3 in two families with CZP3 detected distinct sequence changes that were not present in a panel of 105 normal, unrelated individuals. In family B, an A-->G transition resulted i n an asparagine-to-serine substitution at codon 63 (N63S) and introduced a novel MwoI restriction site. In family E, insertion of a C at nucleotide 11 37 (1137insC) introduced a novel BstXI site, causing a frameshift at codon 380. Restriction analysis confirmed that the novel MwoI and BstXI sites cos egregated with the disease in families B and E, respectively. This study id entities GJA3 as the sixth member of the connexin gene family to be implica ted in human disease, and it highlights the physiological importance of gap -junction communication in the development of a transparent eye lens.