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.
Babies with the XX male syndrome may come to medical attention at birth because of hypospadias or because of cryptorchidism (undescended testes). However, most individuals with the syndrome have a normal penis and their testes in the scrotum and do not come to medical attention until after puberty. Other symptoms include small testes, gynecomastia and sterility. Many individuals with this condition also have feminine characteristics.
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.
In XX male syndrome caused by the gene SRY, the condition is caused by a translocation between the X chromosome and Y chromosome. The translocation occurs when part of one chromosome breaks off and switches places with part of another chromosome. In XX male syndrome, the tip of the Y chromosome that includes SRY is translocated to the X chromosome. As a result, an embryo with XX chromosomes with a translocated SRY gene will develop the physical characteristics of a male. Typically, a piece of the Y chromosome in the pseudoautosomal region exchanges with the tip of the X chromosome. In XX male syndrome, this crossover includes the SRY portion of the Y.
XX male syndrome occurs in approximately one in 20,000 to one in 25,000 individuals. The vast majority, about 90%, has SRY detectable in their cells. The remaining 10% are SRY negative, although some research indicates that up to 20% can be SRY negative. XX male syndrome can occur in any ethnic background and usually occurs as a sporadic event, not inherited from the person's mother of father. However, some exceptions of more than one affected family member have been reported.
For those with XX male syndrome with normal male genitals and testicles no treatment is absolutely necessary. If the child is born with hypospadias or undescended testicles one or more surgeries to correct the condition may be required. If discomfort due to gynecomastia is severe enough, breast reduction surgery may be chosen. The rare person with true hermaphrodism usually requires surgery to remove the gonads, as they can become cancerous. Men with XX male syndrome have normal intelligence and a normal life span. However, all affected men will be infertile.
There are a number of other syndromes related to the karyotype of the sex chromosomes, such as XYY syndrome, Turner syndrome (patients have one X and no Y chromsome), Klinefelter syndrome (patients have two X chromosomes and one Y), Triple-X syndrome (patients have three X chromosomes), etc.
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- de la Chapelle A (1972). "Analytic review: nature and origin of males with XX sex chromosomes". Am J Hum Genet 24 (1): 71â€“105. PMID 4622299.
- Vorona E, Zitzmann M, Gromoll J, SchÃ¼ring 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): 3458â€“65. doi:10.1210/jc.2007-0447. PMID 17579198.
- http://www.healthline.com/galecontent/xx-male-syndrome Healthline.com: XX Male Syndrome