Turner syndrome

Last revised by Patrick O'Shea on 14 May 2024

Turner syndrome, also known as 45XO or 45X, is the most common of the sex chromosome abnormalities in females. 

The incidence is estimated at 1:2000-5000 of live births, although the in utero rate is much higher (1-2% of conceptions) due to a significant proportion of affected fetuses aborting by the 2nd trimester

Individuals with Turner syndrome have greater risk of autoimmune disease than the general population, leading to increased rates of type 1 diabetes mellitus, inflammatory bowel disease, hypothyroidism and other autoimmune diseases in this cohort 9.

The cardiovascular anomalies commonly seen in Turner syndrome (e.g. aortic coarctation, bicuspid aortic valve) lead to increased prevalence of systemic hypertension in affected patients.

See the Radiographic Features section below for a full discussion of the anomalies associated with Turner syndrome.

In adults, Turner syndrome is one of the most important causes of primary amenorrhea and accounts for approximately one-third of such cases. The associated ovarian dysgenesis typically leads to absence of secondary sex characteristics. Intellectual development is unaffected in Turner syndrome.

Turner syndrome is classically characterized by the absence of one X chromosome copy (45 XO), with the missing chromosome most frequently (two-thirds) being the paternal one. Most cases occur as a sporadic event.

However, the classic genetic change is not present in all cases. Three main subtypes include:

  • complete monosomy (45XO): ~60% 

    • even though it is relatively common, almost all 45 XO fetuses will spontaneously abort, with 70% lost between 16 weeks and term

  • partial monosomy (structurally-altered X chromosome): ~15%

  • mosaicism (XO and another sex karyotype): ~30%

Unlike the common trisomies, there is no association with maternal age.

In utero complications include:

  • development of hydrops fetalis: usually from fluid overload secondary to lymphatic failure

People with Turner syndrome are also at 2x risk of autoimmune diseases compared to the general population such as 9:

The prognosis of Turner syndrome is highly variable depending on the presenting associated anomalies. While the vast majority of fetuses are aborted in the second trimester, others may have a long life expectancy. Premature death is commonly due to associated cardiovascular disease.

Patients displaying genetic mosaicism tend to have a more favorable prognosis.

It is named after the American endocrinologist Henry H Turner (1892-1970) 7 who first described the syndrome in 1938.

General differential considerations include:

  • Noonan syndrome: can have similar phenotypical features but normal karyotype

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