Hypohidrotic ectodermal dysplasia caused by an intragenic duplication in EDAR

Hypohidrotic Ectodermal Dysplasia is a syndrome with hypotrichosis, hypohidrosis, and hypodontia as the main symptoms. The prevalence is estimated to one in 5000–10,000 persons. In 10–15% the disease is caused by pathogenic variants in EDAR, and most of the known causal variants to date are missense or nonsense variants. We present a patient with classic Hypohidrotic Ectodermal Dysplasia and mammary gland aplasia with a duplication within EDAR as the likely cause. The duplication is de novo in the patient, and genome sequencing of DNA extracted from blood has revealed that the duplication is in tandem conformation, most likely entailing an altered EDAR protein with a dominant negative effect. This is to our knowledge the first report of an intragenic duplication in EDAR as causal for Hypohidrotic Ectodermal Dysplasia.