Linkage analysis in a large Spanish family with X-linked retinitis pigmentosa: phenotype-genotype correlation.

X-linked retinitis pigmentosa (XLRP) accounts for 10-25% of RP families and causes the most severe form of the disease in terms of onset and progression. Although three different loci (RP3, RP2 and RP15) have been proposed on the short arm of the X-chromosome by linkage analysis, RP3 represents the disease locus in the majority of XLRP families. The identification of female carriers of X-linked RP is important for genetic counselling. The presence of fundus and electroretinogram (ERG) abnormalities have been reported to be as high as 87 and 90%, respectively. However, in clinical practice it has not always been possible to know the carrier state of females at risk. Thirty-five members of a Spanish family with X-linked RP were evaluated by linkage analysis using nine polymorphic markers (CYBB, DXS1110, M6, DXS6679, DXS1068, DXS1058, MAOA, MAOB and DXS6849) that map to the X-chromosome region Xp21.1 to Xp11.3, in an attempt to determine the carrier state of these females at risk. It was possible to establish that a RP3 mutation is, most likely, segregating in this family.