CARRIER DETECTION IN X-LINKED RETINITIS-PIGMENTOSA

X-linked retinitis pigmentosa (XLRP) is manifested in affected males i n their first decade and results in blindness by the third or fourth d ecade. Carrier detection is difficult since most carrier females show no or only equivocal signs well into or beyond their reproductive year s. The genes, or the mutations causing RP have not been identified but at least two have been localised to the short arm of the X chromosome provisionally named RP2 and RP3. Identifying inheritance of one or ot her of these genes must be done by linkage in families using close, in formative DNA markers. Here we report the localisation of a highly inf ormative polymerase chain reaction (PCR) detectable microsatellite mar ker DXS538 using a previously studied family with X-linked RP3 in whic h recombination had occurred in the region of importance. The DXS538 d inucleotide repeat locus was previously localised to Xp21.1-p11.21 to study RP3 in one XLRP family. Using published RFLP data we narrowed th e localisation of DXS538 to the region Xp21.1-p11.23. Thus DXS538 is n ow a convenient diagnostic tool, aiding carrier detection of XLRP in f emales, as shown in the family presented here.