This study is being done to collect information about people who have or may have Hypohidrotic Ectodermal Dysplasia (HED) or X-linked Hypohidrotic Ectodermal Dysplasia (XLHED). This study will allow Edimer Pharmaceuticals to know more about HED/XLHED so that hopefully the investigators can develop a drug to treat this condition. In this study Edimer will retrospectively review and abstract (summarize) medical records of people that have or may have HED/XLHED in order to further understand the natural history and disease characteristics.

Inclusion Criteria:

-Males or females with:

1. the clinical characteristics of HED, including at least two of the following characteristics: a history of decreased sweating;abnormal teeth (fewer permanent teeth, teeth are smaller than average and often have conical crowns);sparseness of scalp and body hair.

   -OR-

2. genetically confirmed HED or XLHED;

The study will enroll up to fifty HED/XLHED affected individuals.