XYY syndrome

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XYY syndrome, also known as Jacobs syndrome and Superman syndrome, is an aneuploid genetic condition in which a male has an extra Y chromosome. There are usually few symptoms. These may include being taller than average and an increased risk of learning disabilities. Most individuals with this condition have normal fertility. The condition is generally not inherited but rather occurs as a result of a random event during sperm development. Diagnosis is by a chromosomal analysis, but most of those affected are not diagnosed within their lifetime. There are 47 chromosomes, instead of the usual 46, giving a 47,XYY karyotype. The condition occurs in about 1 in 1,000 male births. The vast majority of people with the condition are unaware that they have it. The condition was first described in 1961. Some individuals may be offered speech therapy and outcomes are generally positive.

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