Medical Genetics

Turner syndrome

A sex-chromosome condition caused by complete or partial loss of one X chromosome, usually 45,X or mosaic, with variable short stature, ovarian insufficiency and characteristic cardiac, renal, hearing, metabolic and learning needs; aortic disease makes lifelong cardiovascular care essential.

Definition

Turner syndrome is a sex-chromosome condition caused by complete or partial absence or structural abnormality of one X chromosome. The commonest karyotype is 45,X, but mosaic and structural variants produce a variable phenotype involving growth, ovaries, cardiovascular, renal, hearing, metabolic, skeletal and neurodevelopmental systems.

First principles

Loss of X-chromosome dosage affects growth and ovaries

Some X-chromosome genes escape inactivation and are normally present in two copies. Loss or structural change of one X reduces dosage, including of SHOX, contributing to short stature, while accelerated loss of ovarian germ cells causes gonadal dysgenesis, oestrogen deficiency and infertility in most people.

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