Turner's syndrome is caused by the absence of one
of the sex chromosomes, monosomy of X chromosome.
Cells contain only 45 chromosomes with a single X
chromosome, rather than the usually 46XX in a female
or 46XY in a male. Half of Turner's syndrome cases
have karyotype 45XO (i.e. single X chromosome) and
the remainder have one normal X and one abnormal
chromosome (partial deletion, ring formation or short/long
iso-chromosomes). Turner's syndrome occurs sporadically,
and there is no association with increased maternal
age as it arises from mitotic, not meiotic, error.
Having an affected child does not appear to alter
the risk in subsequent pregnancies.
Generally all cases of monosomy except Turner's
syndrome are non-viable. Turner's syndrome is frequent
in first trimester spontaneous abortions as most
conceptuses are lethal. The ovaries form normally
until the end of 2nd trimester but do not make primary
follicles, they then degenerate and may not be detected
on ultrasound. Many cases are associated with cystic
hygroma (an accumulation of fluid within the skin
around the fetal neck), this is often present in
association with more general fetal fluid accumulation
with inn other body cavities, such as the fetal chest
(pleural effusion), pericardium (pericardial effusion)
and abdomen (ascites). This general accumulation
of fluid within the fetus is termed "fetal hydrops" and
is an extremely poor prognostic sign, with almost
all cases dying in-utero. At the time of birth, the
fluid within cystic hygromas is usually been reabsorbed,
leading to loose skin and so-called webbing of the
neck. Coarctation of the aorta is also common, as
is growth retardation and asymptomatic renal tract
anomalies (horseshoe kidney, duplex ureters).
Many cases of Turner's syndrome are not diagnosed
until childhood and many present at puberty with
primary amenorrhoea, failure of secondary sexual
development, or short stature with no pubertal growth
spurt. Other features include a broad (shield-shaped)
chest with widely spaced nipples, a low posterior
hairline, hypoplastic or malformed nails, pigmented
naevi, cervical lymphatic cysts, and an increased
carrying angle at the elbow (cubitus valgus). Most
girls are infertile but menstruation and secondary
sexual development can be induced by oestrogen replacement.
Intelligence is within the normal range. Life span
is normal but osteoporosis may develop if oestrogen
replacement is not used.
MIDLANDS DATA To be added.
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