Hypohidrotic ectodermal dysplasia.

Hypohidrotic ectodermal dysplasia A CLARKE Regional Genetics Advisory Service, Newcastle upon Tyne NE2 4AA.Hypohidrotic ectodermal dysplasia (HED) is an uncommon X linked condition.The phenotype includes sparse scalp hair, largely absent body hair, deficiency of the eccrine sweat glands, and anodontia or oligodontia with conical teeth (figs 1 to 3).There is often a distinctive facies, with prominence of the forehead, a depressed nasal bridge, prominent lips, and periorbital wrinkling and pigmentation.Sub- cutaneous fat is often diminished or absent, as are the mucous glands in the respiratory tree and the gastrointestinal tract.HED was first described in 1848 by Thurnam,' and later in the 19th century by Darwin.2It was assigned to the X chromosome in 1921 by Thadani, who later reported that the carrier females could manifest signs of the condition.4The full significance of this was not appreciated until Mary Lyon hypothesised the random inactivation of one X chromosome in each female cell early in embryo- genesis.Incidence HED is found in all racial groups and in all areas of the world.The incidence at birth was estimated by Stevenson and Kerr,6 based on the prevalence of HED in Oxfordshire: they suggested a rate of 1 per 100 000 births.Personal experience would support this estimate.