The ectodermal dysplasias are a group of hereditary conditions characterized by abnormal hair, teeth, fingernails and toenails, and sweat glands.
All ectodermal dysplasias have a genetic etiology and involve abnormal development and growth of tissues derived from the ectoderm. The ectoderm is the outermost layer of the developing embryo, which gives rise to the hair, teeth, nails, and skin. More than 100 different ectodermal dysplasia conditions have been described in the medical literature. The most common of these is hypohidrotic ectodermal dysplasia, which may account for up to 80% of all ectodermal dysplasias.
Other ectodermal dysplasia conditions include ectrodactyly-ectodermal dysplasia-clefting (EEC) syndrome, hidrotic ectodermal dysplasia (Clouston syndrome), Hay-Wells syndrome, incontintentia pigmenti, Rapp-Hodgkin syndrome, tricho-dento-osseous syndrome, and tooth-nail (Witkop) syndrome. Each of these conditions appears to account for 1–4% of all ectodermal dysplasias.
Most ectodermal dysplasia conditions are associated with sparse hair that has abnormal texture. The hair may appear thin, dry and brittle. In some cases, premature balding may occur.
The teeth of those with ectodermal dysplasia are typically abnormal and reduced in number. A characteristic conical and sharply pointed tooth shape is often present. In some cases, the majority of teeth are missing.
In some ectodermal dysplasia conditions, the fingernails and toenails may be absent or abnormally formed. The nails may be thickened, thinned, brittle, or display unusual ridging or pitting.
The skin may be thin, show abnormal pigmentation, and be prone to eczema (a condition of dry skin characterized by inflammation and itching). The nasal and respiratory passages may be dry, leading to abnormal discharges and increased infections. In hypohidrotic ectodermal dysplasia, the sweat glands are reduced in number, which may lead to dangerous hyperthermia (high body temperature).
Other abnormalities that may occur in the ectodermal dysplasia conditions include amastia (absent mammary glands), cleft lip and/or palate, ectrodactyly (split hand or split foot), and abnormal bands of skin in the mouth or connecting the eyelids.
Many individuals with ectodermal dysplasia have normal cognitive function. A minority of cases may involve some degree of mental retardation. In the case of hypohidrotic ectodermal dysplasia, untreated hyperthermic episodes can lead to brain damage and cognitive impairment.
Jennifer Ann Roggenbuck MS, CGC, Thomson Gale, Gale, Detroit,