Dictionary of Human Evolution and Biology

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Turner Syndrome

Nonfamilial aneuploid condition (2N 45, X0); clinical symptoms in these females include low birth weight, swelling in hands and feet, webbing of the neck, coarse facial features, nail hypoplasia, and a very low hairline in childhood; there is no sexual maturity (gonadal dysgenesis and sterility are nearly universal). Further symptoms include a short adult stature, wide-spaced nipples, broad chest, and pigmented moles; hearing impairment prevalence ranges from 50 to 100%. There is an excess of lymphocytes at all stages of cases. There is no reported parental age effect. Rare cases of phenotypic sex discordance sometimes involve originally male MZ twins with subsequent somatic nondisjunction in one of the pair that produces a 45,X0 female phenotype; the other twin remains a normal male. Recently developed hormonal therapy techniques can produce a near-normal phenotype. Turner syndrome exhibits evidence for genomic imprinting; it is usually the father’s X chromosome that is lost. 1: 2,500 live-born females affected; 1% of all conceptions are 45,X0, but 98% of all X0 conceptuses are spontaneously aborted, which indicates that the condition is frequent at conception (1: 250).

See primary nondisjunction.

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