In a collaborative research, with support from the US-based National Institute of Health (NIH), a team of scientists from the institute have done chromosomal analysis of the defective gene that causes `zonular congenital cataract', the common form of eye disease in families that have a tradition of marriages with close relatives.

``The incidence of hereditary blindness is more common in South India, particularly Andhra Pradesh and Karnataka, because of such tradition. We have located the defective gene on the eleventh chromosome,'' Dr D Balasubramanian, Director, Research, Hyderabad Eye Research Foundation of the LVPEI, said.

A family from Andhra Pradesh with hereditary cataract running in three generations was studied. After detailed clinical, ophthalmological examinations and gene analysis, it was found that allthe affected family members showed a zonular cataract characterised by a y-shaped opacity in the eye lens, he said.

``We could identify and locate the gene responsible for making the proteins of eye lens defective and reflected directly as opacity of the lens'', Balasubramanian, the former director of the Centre for Cellular and Molecular Biology (CCMB) here, said.

The research project is a joint effort by LVPEI, the Department of Genetics of Osmania University here and the CCMB, Balasubramanian said.