Individuals with X-linked hypohidrotic ectodermal dysplasia (XLHED) lack a normal sweat response, placing them at life-long risk for severe overheating. This study reports on the use of non-invasive technologies for assessing sweat gland function, and correlated the results with the nature and location of EDA gene defects underlying XLHED. In contrast to previous reports on mixed patient populations, the data confirmed a consistent, quantifiable defect of sweat gland function in male XLHED subjects as a disease biomarker. Specific mutations present in 60% of the male patients were associated with a total absence of sweating, and all remaining subjects had reduced sweat rates. These findings imply that systematic mapping of EDA mutations together with the analysis of objective clinical data may help to distinguish functionally crucial mutations from those allowing residual activity of the gene product. (By Dr. Holm Schneider, http://jmg.bmj.com/content/early/2011/02/26/jmg.2010.084012.abstract?papetoc= )