Consanguinity and ocular genetic diseases in South India: analysis of a five-year study.

OBJECTIVE: Consanguineous marriage is a widely practised social custom in Asia and northern Africa. In south India, Dravidian Hindus have contracted consanguineous marriages for over 2,000 years. In the present study, the influence of consanguinity on the prevalence of visual disorders was examined in patients attending a specialist genetic eye clinic. SUBJECTS AND METHODS: A total of 2,335 patients attending Sankara Nethralaya, Chennai, India, were screened for genetic eye disorders over a five-year period. The patients were drawn from all parts of India and from neighbouring countries in south Asia. RESULTS AND DISCUSSION: Six hundred and seventy-three (28.8%) of the patients tested for ophthalmic genetic disorders reported a family history of consanguinity. The majority (n = 574) of these families were from south India. In the patient group as a whole, the most common form of consanguineous union was between first cousins (n = 367), followed by uncle/niece marriage (n = 177), equivalent to a mean coefficient of inbreeding alpha = 0.0202. Among the consanguineous families, 430 of 673 (63.9%) had retinitis pigmentosa, 167 of these cases were autosomal recessive and 199 were isolated cases. The public in regions such as south India should be made aware of the merits and demerits of consanguineous marriages.