Turner Syndrome

Descriptive text is not available for this imageBASICS

DESCRIPTION

Presence of typical findings in a phenotypic female with one X chromosome and complete or partial absence of the second sex chromosome

EPIDEMIOLOGY

Prevalence: 1:2,000 to 4,000 liveborn females

RISK FACTORS

Genetics

  • Genotype frequencies
    • 45,X 45%
    • 45,X/46,XX 20%
    • 46,Xi(Xq) 15%
    • 45,X/46,XY 10%
    • 46,Xr(X) 5%
    • Other 5%
  • Recurrence risk is low in subsequent pregnancies in the absence of familial X chromosome defects.

PATHOPHYSIOLOGY

  • Fetuses with Turner syndrome have accelerated loss of germ cells from the second half of gestation through the first few years of life, with eventual gonadal failure.
  • Fetal lymphedema leads to many phenotypic features, including neck webbing, low posterior hairline, displacement of the external ears, nail abnormalities, and persistent lymphedema of the hands and feet.
  • SHOX gene deletion at Xp22.33 is responsible for most of the observed height deficit.
  • Individuals with Turner syndrome have a generalized arteriopathy that includes dilation of larger conduit arteries and increased intimal media thickness.

COMMONLY ASSOCIATED CONDITIONS

  • Short stature (~100%)
  • Hypogonadism (90%)
  • Decreased bone mineralization (50–80%)
  • Elevated liver enzymes (50–80%)
  • Middle ear infections (60%)
  • Failure to thrive in the 1st year (50%)
  • Hypertension (50%)
  • Abnormal electrocardiogram (ECG) (50%)
  • Glucose intolerance (15–50%)
  • Nonverbal learning disorder (40%)
  • Bicuspid aortic valve (14–34%)
  • Hearing loss (30%)
  • Autoimmune thyroiditis (15–30%)
  • Attention-deficit/hyperactivity disorder (ADHD) (25%)
  • Myopia (20%)
  • Renal collecting system abnormalities (15%)
  • Strabismus (15%)
  • Aorta coarctation (11%)
  • Horseshoe kidney (10%)
  • Type 2 diabetes (10%)
  • Celiac disease (8%)
  • Aortic dissection (1–2%)

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