Turner syndrome

Last revised by Dr Daniel J Bell on 29 Jul 2021

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 fetuses with 45X aborting by the 2nd trimester

In adults, it is one of the most important causes of primary amenorrhea and accounts for approximately one-third of such cases. 

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

Overall prognosis very variable is dependent on associated anomalies. While the vast majority of fetuses are aborted in the second trimester, some may have a long life expectancy. Cases with mosaicism do much better. Mental development is unaffected.

Premature death is common due to associated cardiovascular disease

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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Cases and figures

  • Case 1: short 4th metacarpal and Madelung deformity
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  • Case 2: with short 4th metacarpal
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  • Case 3
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  • Case 4
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  • Case 5: antenatal - with cystic hygroma and DWM
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