EDA and X-linked hypohidrotic ectodermal dysplasia: EDA gene mutations are widely studied in X-linked hypohidrotic ectodermal dysplasia (XLHED) and anhidrotic/hypohidrotic ectodermal dysplasia (HED), which is the most common genetic disorder of ectodermal development in humans resulting in hypotrychosis, hypodontia, heat intolerance, dry skin and dry eyes, the susceptibility to airway infections and crusting of various secretions.