• USH2A
• usherin
• retinitis pigmentosa
• mutational spectrum

Retinitis pigmentosa (RP), which occurs in about one in 3000–7000 people in Spain, is inherited in an autosomal dominant manner in 12% of cases, in an autosomal recessive way in 39%, and in an X linked manner in 4% of cases. This leaves 41% of RP cases with a simplex form and 4% in which the transmission pattern is unclear.¹

Direct analyses of rhodopsin, the alpha and gamma subunits of rod cGMP-phosphodiesterase, periferin/RDS, rod outer segment membrane protein, recoverin, guanilate cyclase activating protein, S antigen, interstitial retinol binding protein, and NRL have failed to detect any disease causing mutation in non-syndromic ARRP Spanish families. Mutations in the beta subunit of the rod cGMP-phosphodiesterase gene,^2–5 in the ATP binding cassette receptor gene,⁶ and in the TULP1 gene⁷ account for a small percentage of Spanish ARRP families. These data indicate that genes other than these may be involved in the remaining families, emphasising the genetic heterogeneity of the disease and reinforcing the hypothesis that in ARRP a number of genes rather than one major gene will account individually for a small number of cases.

The recent report that a missense mutation in the USH2A gene (C759F) is present in 4.5% of patients with non-syndromic ARRP⁸ prompted us to analyse the involvement of this mutation in a large set of Spanish ARRP families. A complete mutational analysis of the coding region of the USH2A gene was performed in all cases in which the C759F allele was found. Additional mutations were identified in the USH2A gene in non-syndromic ARRP patients. Interestingly, two C759F homozygotes belonging to a consanguineous ARRP family had no RP symptoms and no hearing impairment.