Turner Syndrome

Pathophysiology

Absence of one set of genes from the short arm of one X chromosome:

  • Most are 45XO, missing paternal X chromosome
  • Also may have present but dysfunctional 46X, i.e. 46 XXiq
  • Mosaic: 45XO,46 XX or 45XO,46XY

SHOX = short stature homeobox gene. Usually present on both X and Y chromosomes, so Turner's have one instead of two. ?presence in growth plates explains diminished stature in TUrner's.

Frequency

Approximately 1 in 2000 live-born female infants. As many as 15% of spontaneous abortions have a 45 X karyotype.

Clinical features

  • Short stature. Growth often in normal range but below 50th centile before age 11; virtually absent growth spurt. Scoliosis in 10% contributes to shortness.
  • Ovarian failure (suspect if no breast development by age 12 or no menses by age 14). Raised gonadotrophins.
  • Infertility except mosaics.
  • Cardiac abnormalities - coarctation, bicuspid aortic valve, aortic root dilatation predisposing to dissection.
  • Gonadal malignancy - common in people with 45-XO, 46-XY mosaicism. Streak gonads, anywhere between usual position of ovaries and inguinal canal, may develop. Gonadoblastoma is the typical result.
  • Horseshoe kidneys
  • Hypothyroidism - about 50% are antibody +ve and 10-30% develop thyroid failure.
  • Deafness
  • Lymphoedema plus hypoplastic nails can give sausage-like appearance to fingers.
  • Webbed neck due to lymphoedema in utero.
  • Increased carrying angle (cubitus valgus) due to abnormal trochlear head development. Raised incidence of congenital dislocation.
  • Short 4th metacarpal or metatarsal - no clinical significance.
  • Shield chest - broad with widely-spaced nipples.

Management

Growth hormone

  • Widely used, achieves some improvement in adult height - various estimates, but about 6cm extra height is typical. Untreated height usually < 5 feet.
  • Double standard GH-deficient dose is used, because Turner's patients may be growth hormone resistant.

Oestrogen/progestogen replacement

  • Induces fusion of epiphyses, therefore generally postponed until after GH treatment.
  • Start at low dose, e.g. 2mcg/day ethinyloestriadiol at age 10 (or whenever gonadotrophin rise detected) to gradually induce puberty (unusual appearances possible if high-dose oestrogen started early). Build up e.g. yearly 2-4-6-8-10 mcg/day. Change to standard OCP e.g. Loestrin 20 once break-through bleeding or age 15-16.
  • Nabhan et al suggest that transdermal oestrogen is more efficacious than oral (though not clear if doses were equivalent).

Other

  • Confirm karyotype in all cases - gonadectomy is mandatory if any 46-XY mosaicism.
  • Renal ultrasound for horseshoe kidney.
  • Assess for coarctation and hypertension
  • Echocardiography for aortic root abnormalities - 5-yearly in Metabolic Unit handbook, some recommend MRI.
  • DEXA - MU handbook recommends 5-yearly, though note that usual reference ranges do not apply.
  • Annual TFTs
  • Gonadectomy if Y remnant
  • Audiogram