Klinefelter's syndrome

Klinefelter syndrome (KS), also known as 47,XXY, is a chromosome anomaly. Subjects affected by the condition are almost always phenotypically male, with common complications such as infertility and small, poorly functioning testicles. Although this is one of the most common chromosomal disorders, symptoms are often noticed only at puberty. The birth prevalence of KS in the State of Victoria, Australia, was estimated to be 223 per 100,000 males. It is named after American endocrinologist Harry Klinefelter, who identified the condition in the 1940s, along with his colleagues at Massachusetts General Hospital. The syndrome is defined by the presence of at least two X chromosomes in addition to a Y chromosome, yielding a total of 47 or more chromosomes rather than the usual 46. Sometimes certain chromosome anomalies like 48,XXXY, 48,XXYY or 49, XXXYY are considered variants of Klinefelter syndrome. Klinefelter syndrome occurs randomly. An older mother may have a slightly increased risk of a child with KS. The syndrome is diagnosed by the genetic test known as karyotyping.