X/Y translocation in a family with X-linked ichthyosis, chondrodysplasia punctata, and mental retardation: DNA analysis reveals deletion of the steroid sulphatase gene and translocation of its Y pseudogene.

We describe a family with two male members showing an X/Y translocation (karyotype: 46,Y,der(X)t(X;Y)(p22;q11]. At physical examination both patients showed ichthyosis, mental retardation and dysmorphic features. Chondrodysplasia punctata and short stature were present in one case. Direct DNA analysis, using a steroid sulphatase cDNA probe, was performed in one patient, his mother and sister, both carriers of the translocation. We found that the translocated region of the Y chromosome includes the steroid sulphatase pseudogene. These results suggest that in our patients the X/Y translocation may be derived from a recombinational event between homologous regions located on the short arm of the X chromosome and the long arm of the Y chromosome. Clinical and molecular studies on the present family add further information for the construction of a tentative physical map of the distal Xp.