General Medical Information

X Chromosome

Joe Leigh Simpson

In addition to genes on the Y chromosome, various clinical disorders indicate that testicular differentiation also requires loci on X. The importance of genes on the X has long been evidenced by existence of an X-linked recessive form of XY gonadal dysgenesis. Xp also contains a region that, if duplicated, suppresses testicular development despite the presence of SRY. This phenomenon was first recognized by Bernstein, and since then other cases have been reported. The duplicated region responsible for this phenomenon has been called dose-sensitive sex reversal (DSS), and the actual gene DAX-1. The sex reversal (male to female) appears to be the result of duplication and not disruption, given molecular analysis showing breakpoints encompassing the entire region believed to include the gene. The locus is near that of adrenal hypoplasia congenita (AHC), but the exact relationship between AHC and DSS remains obscure.