Close genetic linkage between X-linked retinitis pigmentosa and a restriction fragment length polymorphism identified by recombinant DNA probe L1.28.

Retinitis pigmentosa (RP) is a group of retinal degenerations characterized by progressive visual field loss, night blindness and pigmentary retinopathy1. Its prevalence is in the region of 1–2 in 5,000 of the general population, making it one of the commoner causes of blindness in early and middle life2,3. Although 36–48% of RP patients are isolated cases, the remainder show autosomal dominant, autosomal recessive or X-linked modes of inheritance4,5. The X-linked variety (XLRP) is found in 14–22% of RP families in the UK2,5. In the present study, X chromosome-specific recombinant DNA probes which can detect restriction fragment length polymorphisms have been used to localize the XLRP gene(s) to a subregion of the X chromosome using linkage analysis. One of the probes, L1.28, has been shown to be closely linked to XLRP in five kindreds,, with 95% confidence limits of 0–15 centimorgans (maximum LOD score of 7.89 at a distance of 3 centimorgans). This suggests that the XLRP locus lies on the proximal part of the short arm of the X chromosome. This probe is potentially useful for carrier detection and early diagnosis in about 40% of cases, provided that genetic heterogeneity can be excluded by analysis of further families.