Ectodermal dysplasia: A genetic disorder in which the skin and associated structures (the hair, nails, teeth, and sweat glands) develop abnormally. X-linked anhidrotic (nonsweating) ectodermal dysplasia is most common; because it is an X-linked trait, it mainly affects males. There is also an autosomal dominant form that affects both males and females. The term ectodermal dysplasia refers to the abnormal development (dysplasia) of structures derived from one of the germ cell layers in the embryo (ectoderm).
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