Genetic Analysis ofaKindred withX-linked MentalHandicap and Retinitis Pigmentosa

Summary Akindred isdescribed inwhich X-linked nonspecific mental handicap segregates together with retinitis pigmentosa. Carrier females arementally normal butmayshowsigns oftheX-linked retinitis pigmentosa carrier state andbecomesymptomatic intheir later years. Analysis ofpolymorphic DNA markers atnineloci ontheshort armof theXchromosome shows that nocrossing-over occurs betweenthedisease andXpllmarkers DXS255, TIMP, DXS426, MAOA,andDXS228. The90%confidence limits showthat thelocus isintheXp2l-q21 region. Haplotype analysis isconsistent withthecausal genebeing located proximal totheXp2lloci DXS538and5'-dystrophin ontheshort armoftheX chromosome. The posterior probability oflinkage totheRP2region ofthe X chromosome short arm(Xpll.4-pll.23) is.727, suggesting thepossibility ofacontiguous-gene-deletion syndrome. Nocytogenetic abnormality hasbeenidentified.