Review Question - QID 107003

The chromosomal analysis revealed a karyotype of 45,XO which is diagnostic of Turner Syndrome (TS). The infant will be born with streak ovaries.

TS typically results from nondisjunction during meiosis I. The lack of the second X chromosome leads to abnormal sexual differentiation due to nonfunctional streak ovaries, which do not produce any estrogen. The lack of estrogen leads to an increase of FSH and LH resulting in primary amenorrhea, infertility, and delayed sexual maturation. Unlike other chromosomal abnormalities (e.g. Down syndrome), affected individuals are born with normal intelligence. Serum AFP may be normal or mildly elevated in Turner Syndrome, although abnormally high levels may indicate that the fluid was incorrectly drawn from a cystic hygroma.

Loscalzo reviews TS and discusses the diagnosis which is both based on clinical features and chromosomal analysis. The female must be missing all or part of the second sex chromosome and display features of TS such as short stature, streak ovaries, lymphedema of the hands and feet, and webbed neck.

Elsheikh et al. review TS and discuss its epidemiology. They estimate that TS affects 3% of female fetuses with only 1% of those surviving and is responsible for 7-10% of spontaneous abortions. The incidence is said to be 1 in 2,500 live female births with the prevalence numbering 1.5 million females affected.

Illustration A demonstrates the classic webbed-neck feature of TS.
Illustration B demonstrates the karyotype of TS (45,XO). Notice the absence of the second X chromosome.

Incorrect answers:
Answer 1: Individuals born with Turner syndrome are born with normal intelligence.
Answer 2: Individuals born with Down syndrome are born with macroglossia.
Answer 3: Individuals born with Edwards syndrome are born with micrognathia.
Answer 4: Individuals born with Patau syndrome are born with cystic kidneys.