XX male syndrome

XX male syndrome
Other names	De la Chapelle syndrome[1]
Human karyotype 46 XX
Specialty	Medical genetics

XX male syndrome, also known as de la Chapelle syndrome, is a rare condition in which an individual with a 46,XX karyotype develops a male phenotype.^[2] Synonyms for XX male syndrome include 46,XX testicular difference of sex development (or 46,XX DSD)^[3][4][5][6]

In 90 percent of these individuals, the syndrome is caused by the Y chromosome's SRY gene, which triggers male reproductive development, being atypically included in the crossing over of genetic information that takes place between the pseudoautosomal regions of the X and Y chromosomes during meiosis in the father.^[2][7] When the X with the SRY gene combines with a normal X from the mother during fertilization, the result is an XX male. Less common are SRY-negative XX males, which can be caused by a mutation in an autosomal or X chromosomal gene.^[2] The masculinization of XX males is variable.

This syndrome is diagnosed and occurs in approximately 1:20,000 new-born males, making it much less common than Klinefelter syndrome.^[8][9][10] Medical treatment of the condition varies, with medical treatment usually not necessary. The alternative name for XX male syndrome, de la Chapelle syndrome, refers to Finnish scientist Albert de la Chapelle, who first described the condition.^[11]