What causes Turner Syndrome?

If you have Turner Syndrome, or are a sibling, friend or parent of a girl with Turner Syndrome, you may wonder…what exactly causes someone to be born with Turner Syndrome?

Turner Syndrome is a disorder involving the chromosomes.  A “normal” girl has a 46,XX karyotype and a normal boy has a 46,XY karyotype.  However, an estimated 1 in every 2000 or so girls is born with a 45,XO karyotype…meaning she is missing a second X chromosome.  This is caused by an error during conception.

Many, if not most, girls with Turner Syndrome are actually what is called “Mosaic”.  This means that they have a few cells with a normal 46,XX or even sometimes a normal 46,XY karyotype.  Unfortunately, Mosaicism is not always detected by Karyotype tests.

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