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XX male syndrome
Classification and external resources
OMIM 278850

XX male syndrome (also called de la Chapelle syndrome, for a researcher who characterized it in 1972[1]) is a rare sex chromosomal disorder. Usually it is caused by unequal crossing over between X and Y chromosomes during meiosis.

This syndrome occurs in approximately one in 20,000 to one in 25,000 individuals, making it less common than Klinefelter syndrome.[2][3]



Symptoms include small testes, gynecomastia and sterility. Many individuals with this condition also have feminine characteristics. According to research at the University Of Oklahoma health science centers, most XX males are not stereotypically feminine and are typical boys and men.


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

See also


  1. ^ de la Chapelle A (1972). "Analytic review: nature and origin of males with XX sex chromosomes". Am J Hum Genet 24 (1): 71–105. PMID 4622299.  
  2. ^ Vorona E, Zitzmann M, Gromoll J, Schüring AN, Nieschlag E (September 2007). "Clinical, endocrinological, and epigenetic features of the 46,XX male syndrome, compared with 47,XXY Klinefelter patients". J. Clin. Endocrinol. Metab. 92 (9): 3458–65. doi:10.1210/jc.2007-0447. PMID 17579198.  
  3. ^ XX Male Syndrome


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