Prenatal diagnosis of X-linked choroideremia with mental retardation, associated with a cytologically detectable X-chromosome deletion.

We describe a family in which an X-chromosome deletion is segregating with choroideremia, and X-linked recessive condition. The DNA sequences DXYS1 and DXS3, defined by the probes pDP34 and 19.2 respectively, are absent in the affected male (who is also mentally retarded), and hemizygous in his mother and in his carrier sister, who presented early in pregnancy. Analysis of chorionic villus DNA formed the basis of prenatal exclusion of choroideremia in her male fetus. In three female relatives, studied with late-labelling techniques, the deleted X was preferentially inactivated in 86-100% of cells studied. This family confirms the localisation of the choroideremia locus to within Xq13----21, and places the loci for anhidrotic ectodermal dysplasia and the X-linked immunodeficiencies outside this region.