A study of retinitis pigmentosa in the City of Birmingham. II Clinical and genetic heterogeneity.

SIR, 'We think it useful to add some follow up information to the above papers.' Firstly, since the paper was submitted for publication in May 1984, we have not ascertained, either in the Retina Clinic of the Birmingham and Midland Eye Hospital, or in the Diabetic Clinic of the General Hospital, any further patients with retinitis pigmentosa who had symptoms on prevalence day. We therefore believe that our observations on the prevalence of retinitis pigmentosal are correct. Secondly, we had attempted by examination of relatives to identify the type of retinitis pigmentosa occurring in 12 severely affected male index patients who had no symptomatic relative. Three of the 12 patients were recognised as having X linked retinitis pigmentosa, one did not have X linked disease because his adult daughter was not a carrier, and eight could not be classified. Two of those eight men are now discovered to have X linked disease, as the young sons of a sister and a daughter respectively have become affected. Their mothers were not available for earlier examination. This means that the likelihood of an isolated male with severe retinitis pigmentosa having the X linked form is about 1 in 2. In our whole series (regardless of severity or family history) we now have 21 male index patients out of 74 with X linked disease, an occurrence of about 1 in 3-5. We have not yet encountered a male with X linked retinitis pigmentosa whose mother had healthy retinae.