What is the name of the syndrome where a female has only one X chromosome?

The syndrome in which a female has only one X chromosome is Turner syndrome. It is usually associated with a 45,X karyotype, also called monosomy X, although some people have mosaicism or a partially missing X chromosome.

The missing or altered X-chromosome material affects development in several body systems. Common features include short stature, ovarian insufficiency, delayed puberty, infertility, and characteristic heart or kidney abnormalities. Physical signs can include a webbed neck, low hairline, and swelling of the hands or feet, but symptoms vary considerably.

Turner syndrome is named after American endocrinologist Henry Turner, who described its characteristic clinical pattern in 1938. The chromosomal basis was identified in 1959, when researchers found a 45,X karyotype in a patient with the syndrome.

A common mix-up is Klinefelter syndrome, which generally involves an XXY chromosome pattern in males. Down syndrome involves an extra chromosome 21, while Marfan syndrome is a connective-tissue disorder rather than a sex-chromosome condition.