Turner syndrome

Most cases of Turner syndrome are not inherited. Most commonly, Turner syndrome occurs due to a random event during the formation of an egg or sperm cell in a parent (prior to conception). For example, if an egg or sperm cell mistakenly loses a sex chromosome, and joins at conception with an egg or sperm containing an X chromosome, the resulting child will have a single X chromosome in each cell.

Mosaic Turner syndrome, occurring when a person has some cells with one X chromosome and some cells with two X chromosomes, is also not inherited. This also occurs due to a random event, during early fetal development rather than before conception.

In rare cases, Turner syndrome may be caused by a missing piece (partial deletion) of the X chromosome. A deletion can be inherited from a parent.^[1]

Genetic testing of an affected fetus or child can identify the type of Turner syndrome present and may help to estimate the risk of recurrence. People with questions about genetic testing or recurrence risks for Turner syndrome are encouraged to speak with a genetics professional. Please visit our page on how to find a genetic clinic.

Turner syndrome is caused by a female having one normal X chromosome in each of her cells, while the other sex chromosome is either missing or structurally abnormal. Females without Turner syndrome have 2 full X chromosome in all of their cells, and males have one X chromosome and one Y chromosome. The missing genetic material affects development before and after birth.

Most females with Turner syndrome are missing the second sex chromosome in all of their cells. This is also referred to as having monosomy X. This form results from a random error in an egg or sperm cell prior to conception.

Some females with Turner syndrome have two X chromosomes, but one of them is missing a piece (has a deletion). Depending on the specific gene(s) that are missing, features of Turner syndrome may or may not be present. A deletion may occur sporadically (not inherited) or it may be inherited from a parent.

Mosaic Turner syndrome (when some cells have one X chromosome and some have two sex chromosomes) is caused by a random error in early fetal development (shortly after conception).

It is still unclear exactly which genes on the X chromosome are associated with each feature of Turner syndrome. It is known that the SHOX gene on the X chromosome is important for growth and bone development. A missing copy of this gene is thought to result in the short stature and skeletal abnormalities in many affected women.^[1]