[Clinical case of the month. A male with 46,XX karyotype]

The XX males represent a rare expression of the Klinefelter syndrome associated with hypergonadotropic hypogonadism. Generally the patients are of small stature with normal secondary sexual male features but with small testes and constant sterility. The plasma concentrations of FSH and LH are very high in accordance with the decrease of the testicular function. From the genetic point of view, the XX males may be divided in 3 groups: 1) in 80% of cases, the XX males bear the SRY gene and exhibit a XY translation during the paternal meiosis with the presence of the SRY gene on one of the X chromosomes as a marker of the male differentiation; 2) in 10% of cases, the males are (SRY-)XX; the abnormal development is then due to other genes than the TDF, which, when mutated, can induce sexual male differentiation. The remaining 10% of cases are due to chromosomal mosaïcism with more XX than XY.