Retinitis pigmentosa in India: a genetic and segregation analysis.

Seventy-eight families with retinitis pigmentosa, presenting at the genetic clinic of Sankara Nethralaya, Madras, over a period of 6 months (from April to September 1993), were assessed to determine the different genetic types: 9% were autosomal dominant; 36%, autosomal recessive; 3%, X-linked recessive; 44%, isolated cases and 8%, undetermined genetic type. A high incidence of consanguinity was observed in autosomal recessive (57%) and isolated cases (37%). Segregation analysis showed good agreement in autosomal dominant (chi 2 = 0.864) and recessive families (p = 0.222). The high proportion of autosomal recessive and isolated cases in this study, when compared with other similar studies, is due to the high incidence of consanguineous marriages in the Indian subcontinent.