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.