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.