XX male syndrome

XX male syndrome (also called de la Chapelle syndrome, for a researcher who characterized it in 1972 ) is a rare sex chromosomal disorder. Usually it is caused by unequal crossing over between X and Y chromosomes during meiosis, which results in one or both of the X chromosomes containing the normally-male SRY gene.

This syndrome occurs in approximately four or five in 100,000 individuals, making it less common than Klinefelter syndrome.

Presentation
Symptoms usually include small testes and subjects are invariably sterile. Individuals with this condition sometimes have feminine characteristics, with varying degrees of gynecomastia but with no intra-abdominal Müllerian tissue. According to research at the University of Oklahoma health science centers, most XX males are not stereotypically feminine and are typical boys and men although other reports suggest that facial hair growth is usually poor and libido is diminished, with notable exceptions.

Clinical diagnosis

 * Standard XX karyotype in two tissues (with at least one, or both, containing the male SRY gene)
 * Male external genitalia, sometimes showing hypospadias
 * Two testes which may or may not have descended the inguinal canal. Most XX males have descended testes.
 * Absence of Müllerian tissue

Pathophysiology
Males typically have one X chromosome and one Y chromosome in each diploid cell of their bodies. Females typically have two X chromosomes. XX males have two X chromosomes, with one of them containing genetic material from the Y chromosome, making them phenotypically male; they are genetically female but otherwise appear to be male.