The role of Yp in sex determination: new evidence from X/Y translocations.

A 33-year-old man had azoospermia and tubular atrophy as in the Klinefelter syndrome but short stature. He had a 46,X,t(X/Y) (Xqter lead to p22.3::Yp11 lead to Yqter) translocation and was H-Y antigen-positive. This excludes one of the genes controlling H-Y antigen from the terminal portion of the short arm of the Y chromosome. This case and the two similar ones in the literature indicate that the proximal Yp portion is required for the differentiation of a male gonad. The pattern of X inactivation was random in the patient's fibroblasts, whereas in the lymphocytes the translocated chromosome was preferentially inactivated; comparison with other cases shows that the quantity of Y chromosome material involved in these translocations does not influence the X inactivation patterns. In the three cases with this dicentric translocation the X chromosome centromere is consistently the active one. Our case indicates that the choice of which centromere is inactivated is independent of the replication pattern of the X chromosome. Our patient and a few other relevant cases from the literature confirm that factors controlling height are located on the distal portion of Xp and of Yp.