The use of a DNA marker for carrier diagnosis in an X-linked disorder: Norrie's disease.

We report a family with the X-linked eye disorder Norrie's disease, in which DNA analysis enabled the distinction to be made between female carriers and non carriers. There was perfect cosegregation of the disease gene and the restriction fragment length polymorphism DXS7 which is recognised by the probe L1.28. Adding our data to those already on record, the lod score for linkage between DXS7 and Norrie's disease reaches 5.6, for a recombination fraction of 0.0. We anticipate that DNA testing will become a major investigative tool in genetic counselling.