Ectodermal Dysplasias at a Glance
- A group of inherited disorders characterized by developmental abnormalities in two or more ectodermal structures.
- These include hair, teeth, nails, and sebaceous and sweat glands.
- There may be abnormalities in nonectodermal structures and functions.
- Distinction is based on clinical features, mode of inheritance, and molecular findings.
- Clinically distinct disorders may be due to different mutations in the same gene (allelic heterogeneity), and clinically similar conditions may be due to mutations in different genes (locus heterogeneity).
The ectodermal dysplasias (EDs) are a group of inherited disorders that share in common developmental defects involving at least two of the major structures classically held to derive from the embryonic ectoderm—hair, teeth, nails, and sweat glands. Freire-Maia and Pinheiro1 published an exhaustive review and classification system for these disorders using a numeric system of 1 (hair), 2 (teeth), 3 (nail), and 4 (sweat glands) for characterization. This system has little use in practice, although it did allow for a rational approach to a previously chaotic field. Freire-Maia and Pinheiro laid claim to more than 150 ectodermal disorders in their most recent compilation.2 Several other classification schemes have been suggested. Each has limited clinical application but can help in ordering thinking about these disorders.3,4 In an attempt to move to a more useful and unified system, an international classification conference was convened in 2008 to initiate this process which is still ongoing.5
This chapter covers only the more common of these conditions and those in which ectodermal defects are likely to bring them to a dermatologist for diagnosis and medical attention. Fig. 142-1 is an algorithm showing the approach to the diagnosis of EDs. The first step in the algorithm for making a specific diagnosis of an ED is to determine the presence of sweating (hidrotic) or absence of sweating (hypohidrotic/anhidrotic). The involvement of other ectodermal structures and of nonectodermally derived tissues provides further branching points in a diagnostic hierarchy. Mode of inheritance may differ within a seemingly uniform diagnostic group, and care must be taken in evaluating family members before providing recurrence risks.
Approach to the diagnosis of ectodermal dysplasias. AD = autosomal dominant; ADULT = acro-dermato-ungual-lacrimal-tooth syndrome; AEC = ankyloblepharon filiforme adnatum–ectodermal dysplasia–cleft palate syndrome; AR = autosomal recessive; ED = ectodermal dysplasia; EEC = ectrodactyly–ED–cleft lip/palate syndrome; HED = hypohidrotic ectodermal dysplasia; IM = immune defects; X-LR = X-linked recessive.
Within the last few years, causal genes have been identified for many of the EDs. Given continuing discoveries, the reader is directed to the following resources: http://www3.ncbi.nlm.nih.gov/OMIM (Online Catalog of Mendelian Inheritance in Humans) and http://www.ncbi.nlm.nih.gov/sites/GeneTests (an up-to-date listing of laboratories offering molecular testing). The National Foundation for Ectodermal Dysplasias (http://www.nfed.org) is a lay support group that ...