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- What is marker chromosome?
Marker chromosome is a small segment of supernumerary chromosome, whose
origin cannot be determined by conventional cytogenetic methods. These frag-
ments of chromosomes may arise from autosome or sex chromosomes (X or Y)
and require molecular approaches for definitive characterization. The presence
of marker chromosome in a patient with TS should prompt active search for Y
chromosome material. In addition, presence of marker chromosomes is also
associated with increased risk of developing intellectual disability in these
patients.- How to suspect TS during intrauterine period?
TS should be suspected in a fetus with abnormal features on ultrasonography
including increased nuchal translucency, cystic hygroma, left-sided cardiac
defects, renal anomalies, and growth retardation. In addition, a positive triple or
quadruple test should also raise a suspicion of TS. However, these
ultrasonographic features or biochemical tests are not specific for TS, and a
karyotype should be carried out for confirmation of diagnosis.- How to suspect TS at birth or during infancy?
Turner syndrome can be suspected at birth/infancy by the presence of lymphedema,
webbed neck, low posterior hairline, abnormal auricles, left- sided cardiovascular
anomalies (bicuspid aortic valve and coarctation of aorta), and renal anomalies
(horseshoe-shaped kidney). The skeletal abnormalities associated with TS are not
present at birth; they progressively develop with growth of the child.- How to confirm the prenatal diagnosis of TS?
Karyotype is mandatory for the diagnosis of TS. For cytogenetic analysis, cho-
rionic villous sampling can be performed between 10 and 12 weeks of gesta-
tion, whereas amniocentesis can be performed between 15 and 17 weeks. In
the presence of ultrasonographic abnormalities and 45,XO or mosaicism, the
likelihood of having clinical TS is very high. However, with 45,XO/46,XX
mosaicism without ultrasonographic abnormalities, probability of TS is low.
Hence, karyotype should be repeated after birth in all babies with a prenatal
diagnosis of TS.- What is the cause of webbed neck in Turner syndrome?
Lymphatic aplasia or hypoplasia during intrauterine period results in accumula-
tion of lymph in the jugular lymph sac and consequently, formation of a large
swelling in the neck, i.e., cystic hygroma. Progressive resolution of lymph in
cystic hygroma results in redundant and loose skin around the neck, leading to8 Turner Syndrome