Norrie's disease: delineation of carriers among daughters of obligate carriers by linkage analysis.

Norrie's disease is an X-linked disorder with congenital blindness. Carriers are clinically healthy, so that they are only identifiable when they are daughters of affected males, or mothers to affected males in whose families other males have Norrie's disease. Daughters of carriers have an á priori 50 per cent risk of being carriers themselves. We have recently found close linkage between the genes for Norrie's disease and the DXS7 locus, characterised by a DNA restriction fragment length polymorphism (RFLP), L1.28. In three informative families we show that this RFLP can help to delineate carriers from those of their female relatives who are homozygous for the normal gene.