A patient with ectodermal dysplasia (ED) presents with dry eyes, sparse hair, anodontia, and what appears to be a small head circumference. All of the following are features of ED EXCEPT one. Which is the EXCEPTION?

Correct answer: C. Bifid ribs

• A. Anodontia (complete absence) or oligodontia (partial absence) of teeth — the most clinically significant oral manifestation of hypohidrotic ED, affecting both primary and permanent dentitions.
• B. Sparse or absent hair (hypotrichosis or atrichia) — hair follicles are ectodermal; their absence is a hallmark of ED.
• C. CORRECT. Bifid ribs are NOT a feature of ectodermal dysplasia. Bifid ribs are associated with Gorlin-Goltz syndrome (nevoid basal cell carcinoma syndrome) or Ellis-van Creveld syndrome, not ED. ED features involve structures derived from ectoderm: teeth, hair, nails, and sweat/sebaceous glands — ribs are mesodermal structures.
• D. Dry eyes (lacrimal gland hypoplasia/aplasia) — tear glands are ectodermal derivatives; their absence in ED causes dry eyes and risk of corneal damage.