Clouston's hidrotic ectodermal dysplasia is caused by mutations in a connexin gene, GJB6 or connexin-30, characterized by scalp hair that is wiry, brittle, and pale, often associated with patchy alopecia. Presentation Hidrotic ectodermal dysplasia 2, or Clouston syndrome (referred to as HED2 throughout this entry) is characterized by partial or total alopecia, dystrophy of the nails, hyperpigmentation of the skin (especially over the joints), and clubbing of the fingers. [Source: Wikipedia ]