Klinefelter syndrome

Klinefelter's syndrome is a condition caused by a chromosomal abnormality in males (specifically, a nondisjunction); sufferers have a pair of X sex chromosomes instead of just one. The XXY chromosome arrangement is a common genetic abnormality, occurring as frequently as 1 in 1,000 male births, but the symptoms that may result from having the extra chromosome are less common. Because of this extra chromosome, individuals with the abnormality are usually referred to as "XXY Males" rather than as "suffering from Klinefelter's syndrome."

In mammals with more than one X chromosome, the genes on all but one X chromosome are barred from being expressed. This happens in XXY males as well as XX females. A few genes, however, have corresponding genes on the Y chromosome and are not barred. These triploid genes in XXY males may be responsible for the symptoms of Klinefelter's syndrome.

In adults, the syndrome is characterised by gynecomastia (enlarged breasts), a rounded body type with abnormal body proportions, sparse facial and body hair, small testes, and an inability to produce sperm. Most XXY males have some degree of language impairment as well. The syndrome is associated with an increased risk of breast cancer, pulmonary disease, varicose veins, and osteoporosis.

The condition was identified in 1942 by Dr. Turner syndrome