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Pathology · single question

Ectodermal dysplasia: which structure is NOT typically affected by the patient's genetic condition?

  1. Muscle tone
  2. Hair
  3. Teeth
  4. Skin
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Correct answer: A. Muscle tone

Ectodermal dysplasia (ED) is a group of inherited conditions affecting structures derived from ECTODERM: skin (hypohidrosis, dry skin), teeth (hypodontia, conical teeth), hair (hypotrichosis, thin/brittle hair), nails, sweat glands, and sebaceous glands. MUSCLE TONE is derived from MESODERM and is NOT affected by ectodermal dysplasia. Muscle function and tone remain normal in ED.
  • A. CORRECT (NOT affected). Muscle tone is determined by mesoderm-derived muscle tissue and its neural innervation — neither of these is ectodermal. Muscle tone is NORMAL in ectodermal dysplasia.
  • B. INCORRECT (IS affected). Hair follicles are ectodermal — ED causes hypotrichosis (thin, sparse, brittle hair).
  • C. INCORRECT (IS affected). Teeth are ectodermal derivatives (enamel is from enamel organ; dentin/pulp/cementum from neural crest/mesoderm). In ED: hypodontia, anodontia, peg-shaped/conical teeth.
  • D. INCORRECT (IS affected). Skin is ectodermal in origin — ED causes dry skin, hypohidrosis (reduced sweating), and wrinkled/aged skin appearance.

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