Hypohidrotic ectodermal dysplasia (HED) is caused by mutations in the genes encoding the components of the tumour necrosis factor α (TNFα)-like signalling pathway and is characterised by aberrant differentiation of tooth buds, hair follicles and eccrine sweat glands which leads to the characteristic HED phenotype.

Numerous mutations in the EDA (ectodysplasin-A) gene have been reported while EDA1R (ectodysplasin-1 receptor) or EDARADD (ectodysplasin-A receptor-associated adapter protein) defects are rare. Relatively frequent mutations of NEMO (NF-κ-B essential modulator) detected in HED patients are accompanied by immunodeficiency and incontinentia pigmenti.1 Recently we reported a possibly causative novel mutation of TRAF6 (TNF receptor associated factor6) in a patient displaying mild symptoms typical of HED.2

The most common form of HED is caused by mutations in the EDA which encodes the ligand for specific receptors. Two major isoforms of the EDA gene product, originating from differential splicing of the primary transcript, were detected. Ectodysplasin-A1 (EDA-A1) is recognised by EDA1R leading to the recruitment of an adaptor protein, EDARADD, while ectodysplasin-A2 (EDA-A2), which is shorter than EDA-A1 by two amino acids, is recognised by EDA2R (XEDAR).3

The extracellular domain of XEDAR exhibits 32% …