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New mutations in γ-crystallin (CRYG) genes cause congenital cataracts in Indian families. The discovery, which mirrors the influence of cryg genes in mice, may throw light on how cataracts form.
A study of seven families with an index case of cataract in both eyes in a child identified three point mutations in the CRYG gene cluster. These segregated with cataracts in close relatives of the index case in an autosomal dominant pattern of inheritance. Two mutations were missense mutations in the CRYGC and CRYGD genes. They were associated with lamellar cataracts. One mutation was a nonsense mutation in CRYGD associated with central nuclear cataracts. In four families mutations were not evident in CRYG genes and are yet to be identified.
The index cases were selected from children aged under 15 years presenting to a paediatric eye clinic in southern India with cataracts in both eyes. Mutations were identified by amplification and sequence analysis of the γ-crystallin gene cluster in genomic DNA samples taken from the index cases and their close relatives.
Cataracts in both eyes are more common in Indian children than in other ethnic groups. The γ-crystallin genes are crucial for the development of the lens of the eye as they specify one of its main protein components. Their sequences are highly conserved in a mammals, making them obvious candidates for study.