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Genetics

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

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Turner's syndrome is the result of a sporadic chromosomal abnormality. It can result from the non-disjunction of chromosomes in either parent. Over 99% of 45X0 fetuses abort. The risk of recurrence is low.

A minority of individuals are mosaics 45X0/46XX, or more rarely 45XO/45XY.

Turner's syndrome is the only viable monosomy in humans. This is probably because in normal females one copy of the X chromosome in each cell is functionally inactivated in a process called Lyonisation - leading to formation of the Barr body, the absence of which is a diagnostic feature in Turner's. Thus the normal situation in a cell is to have just one functional X chromosome; it is only in certain tissues that the loss matters.


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