Hypohidrotic ectodermal dysplasia (HED) is a complex genetic disorder characterized by lack of sweat glands, sparse hair, and missing or malformed teeth. Inability to sweat may result in episodes of severe hyperthermia and cause sudden infant death. To assess sweat gland function in HED patients, the investigators will first quantify gland pores in a defined area of the palm and then stimulate the glands by pilocarpine followed by sweat collection in a special capillary for volume determination. This will be combined with non-invasive skin conductance measurement prior and subsequent to stimulation of the sympathetic nervous system. The data should provide a basis for genotype-phenotype correlation.

Inclusion Criteria:

• for patients: hypohidrotic ectodermal dysplasia caused by mutations in the genes EDA or EDAR
• written informed consent

Exclusion Criteria:

• febrile disease
• pregnancy or breastfeeding
• implantable electronic devices, e.g. pacemaker
• hypersensitivity to self-adhesive electrodes

subjects with recessively inherited hypohidrotic ectodermal dysplasia (HED), their heterozygous family members and healthy controls