MULTICENTER GENETIC-STUDY OF RETINITIS-PIGMENTOSA IN JAPAN .2. PREVALENCE OF AUTOSOMAL RECESSIVE RETINITIS-PIGMENTOSA

Retinitis pigmentosa (RP) is a group of genetically heterogeneous dise ases with autosomal recessive (AR), autosomal dominant, and X-linked m odes of inheritance. Autosomal recessive retinitis pigmentosa (ARRP) i s the most common form in Japan. A genetic analysis was done to determ ine the prevalence of ARRP indirectly, to provide an estimation of cha nging trends in the overall prevalence of RP. Data on the frequency of consanguinity and marriage year of normal parents of 59 ARRP patients were obtained from a nationwide multicenter survey of typical retinit is pigmentosa conducted in 1990. The gene frequency of ARRP was 0.0114 5 (Dahlberg's formula). In 1990, the number of young symptomatic ARRP patients decreased, while the number of patients aged 40 years and old er increased. The total number of symptomatic ARRP patients in 1990 wa s nearly 21% higher than in 1970. Despite a dramatic decline in consan guinity in recent decades in Japan, the number of ARRP patients has in creased. This increase is attributed to greater longevity and overall population growth. Our results suggest that the total number of RP pat ients has not decreased, and may even have increased. (C) 1997 Japanes e Ophthalmological Society.