An XX male with a single STS gene dose.

There is substantial evidence that many XX males arise from an X/Y interchange, so that a terminal Xp segment carrying the Xg locus, but not the neighboring steroid sulfatase (STS) locus, is replaced by part of the Y chromosome. We show here that one of the two X chromosomes of an XX male with low intracellular levels of STS does not express the STS gene.