Genu valgus

49 XXXXY syndrome

49 XXXXY Syndrome is an extremely rare, aneuploidic sex chromosomal abnormality; its frequency is approximately 1 out of 85,000 to 100,000 males.


As its name indicates, a person with the syndrome has one Y chromosome and four X chromosomes on the 23rd pair, thus having 49 chromosomes rather than the normal 46. As is common with aneuploidy disorders, 49 XXXXY syndrome is often accompanied by mental retardation. It can be considered a form of Klinefelter syndrome, or a variant of it.

It is genetic, but not hereditary. This means that while the genes of the parents cause the syndrome, there is a small chance of more than one child having the syndrome. The probability of inheriting the disease is about 1%.

The individuals with this syndrome are males, but a female version also exists with similar characteristics as the male version.


Aneuploidy is often fatal, but in this case there is "X-inactivation" where the effect of the extra chromosomes would be reduced and thus made safer by the body.

The mental effects of 49 XXXXY Syndrome vary, much like Down syndrome. Males with the syndrome tend to have impaired speech and behavioral problems. Those with 49 XXXXY syndrome tend to exhibit infantile secondary sex characteristics with sterility in adulthood and have some skeletal anomalies. Skeletal anomalies include:

The effects on the males also include:

See also


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