This study in affected Hypohidrotic Ectodermal Dysplasia (HED) males and unaffected male controls, age 1 year and up, will use minimally invasive devices to image sweat ducts in intact skin, to measure stimulated sweat rate, and in a subset of subjects to collect clipped scalp hair samples for RNA analysis. This study is descriptive in nature and is intended to assess the ability to use innovative approaches to generate data from subjects over a wide age spectrum, with particular emphasis on phenotype variability between male siblings (same mutation).