A large Indian family consisting of 5 generations containing 33 affected individuals has been described. This is an autosomal dominant disorder in which a mutation has been found in exon 6 of the CRYBB2 gene (22q11.2-q12/22q11.23). This region contains four crystallin genes as well as the CRYBP1 pseudogene. It has been suggested that gene conversion between exon 6 of the CRYBB2 gene and CRYBR1 may be responsible for the phenotype. Three additional families with identical mutations in the same CRYBB2 exon have been reported and, since each family seems to have a unique phenotype, it is likely that more than a simple bp mutation is responsible for the cataracts.
Some Coppock-like cataracts (604307) also result from mutations in CRYBB2 at the same location but others have mutations in the CRYGC gene. Type 2 congenital cerulean cataracts (601547) have also been associated with mutations in the CRYBB2 gene.
Another autosomal dominant congenital cataract with sutural opacities (600881) has a slightly different phenotype and results from a mutation on chromosome 17.