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of pubarche in children with TS who have ovarian failure. In addition, estrogen
acts in concert with androgens at pilosebaceous unit and induces pubarche.
This also explicits the appearance of pubic hair after initiation of estrogen sup-
plementation in children with TS. The reason for early adrenarche in children
with TS is not known; however, it is postulated that an unidentified factor pro-
duced by ovaries inhibits adrenarche and this is absent in patients with TS due
to gonadal failure (Fig. 8.10).- What is the cause of gonadal failure in TS?
Gonadal failure is present in nearly 95 % of patients with Turner syndrome. It
can present as delayed/arrested puberty, primary amenorrhea, infertility, or
premature ovarian failure. Ovarian development requires two copies of multi-
ple genes present on both short arm (e.g., Xp11) and long arm (e.g., Xq24) of
X chromosome. These genes do not undergo lyonization and hence loss of
even a single copy of these genes will result in streak gonads. In addition,
reactivation of lyonized X chromosome (which occurs at 8 weeks of intrauter-
ine life) is essential for germ cells (oogonia) to enter into meiotic division.
Therefore, absence of one X chromosome in patients with TS results in poor
development of ovaries and accelerated follicular atresia even during intrauter-
ine period.abFig. 8.10 (a) A 20-year-old woman with Turner syndrome. (b) Absence of pubarche in the same
patient
8 Turner Syndrome