This review is focused on recent developments of the genetic studies on anhidrotic ectodermal dysplasia (EDA) reported since the publication of our previous review in 1997. In addition to cloning of the mouse homologue of the EDA gene, the Tabby gene, recent discoveries of the novel transcript isoforms by several research groups as well as by our group, were presented and discussed in the context of the mode of inheritance of anhidrotic ectodermal dysplasia. The paradox that despite typical phenotype, no mutations were evidenced in the originally described two-exon isoform of the EDA gene, was explained. It was also pointed out that despite careful analysis of the structure of the entire gene and its regulatory region, no mutations were found in some of the patients, suggesting the existence of autosomal dominant or recessive forms of the disease, which requires further investigations.
The evidence from literature strongly suggests that Christ Siemens Touraine (CST) syndrome is associated with mutations of the newly discovered EDA gene. The gene is situated on the long arm of the X chromosome (Xq12.2 q13.1) and contains two exons separated by a 200 kbp intron. The 5' untranslated region and most of the coding sequence are localized in exon 1, while three C terminal amino acids are encoded by exon 2. The coding sequence was interrupted by translocations in three affected females: t(X;1), t(X;12), t(X;9), and submicroscopic deletions of the EDA gene were found in five males with CST syndrome, and point mutations were discovered in exon 1 in nine other patients. Northern blot analysis and in situ hybridization studies revealed that the EDA gene was expressed in the foetus, and postnatally in a specific type of skin cell and that the expression was limited to cells of ectodermal origin. A predicted protein product of the EDA gene contains 135 to 140 amino acids, organized in three distinct domains and may belong to class II transmembrane receptors.
Recent developments of the investigations on the molecular basis of anhidrotic ectodermal dysplasia are reviewed. Identification of the major product of the EDA gene (ectodysplasin A), a protein belonging to a group of TNF ligands, and molecular cloning of the cDNA, encoding its receptor (EDAR), a member of the TNF receptor family, are presented. The role of an alternative EDA receptor, localised on the X chromosome (XEDAR) in the developmental control of the differentiation of skin appendages, is discussed. Recent findings have elucidated the cause of the autosomal forms of EDA, both dominant and recessive, and indicated an important role of a signal transduction pathway involving a protein product of the NEMO gene and the transcription factor NFkB in the differentiation of skin appendages.
JavaScript is turned off in your web browser. Turn it on to take full advantage of this site, then refresh the page.