Klinefelter Syndrome

Excerpt

Klinefelter syndrome (KS) results from 2 or more X chromosomes in a phenotypic male. The clinical phenotype of KS was first described by American physician Dr. Harry Klinefelter in 1942. The syndrome describes males with tall stature, small testes, gynecomastia, and azoospermia. The precise genetic etiology of supernumerary X chromosomes (47,XXY) was identified in 1959. Extra X chromosomes lead to testicular hyalinization, fibrosis, and hypofunction, resulting in genital abnormalities, usually hypogonadism, and infertility.

Neurocognitive differences associated with KS began to be recognized in the middle and latter of the 20th century. Often, androgen replacement and neuropsychological and adaptive therapies are beneficial in the medical management of KS. However, deficits in clinical care do exist as there are gaps in diagnosis, lack of standardization of care, and access to treatments can be limited or unaffordable.

A similar but much less common condition, Jacobs syndrome, has the genotype 47,XYY. Affected individuals are phenotypically male. The syndrome is associated with antisocial tendencies, asthma, autism, seizures, some infertility, tall stature, macrocephaly, and hypertelorism. See our companion StatPearls reference article on "Jacobs Syndrome."