The prevalence of X-linked hypohidrotic ectodermal dysplasia (XLHED) in Denmark, 1995-2010

X-linked hypohidrotic ectodermal dysplasia (XLHED) is characterised by hypohidrosis, sparse hair, and teeth abnormalities. Infants with XLHED have an increased risk of death by hyperpyrexia. XLHED is the most common form of hypohidrotic ectodermal dysplasia (HED); however, no population-based prevalence estimates are available. We aimed to: 1) estimate the prevalence of XLHED in the Danish population per January 1, 2011; 2) identify the most frequent age at time of diagnosis; and 3) quantify the most frequent clinical feature associated with XLHED.Materials and methodsWe conducted a nationwide cross-sectional study (1995-2010). We leveraged national medical registries and data from clinical departments to categorise XLHED cases into three groups: 1) Molecularly-confirmed XLHED; 2) Clinically-diagnosed HED (registered with ICD-10 Q 82.4); and 3) Possible HED (registered with sufficient clinical features based on a clinical algorithm that we designed).ResultsWe identified 90 molecularly-confirmed XLHED, 146 clinically-diagnosed HED, and 988 possible HED cases between 1995 and 2010 (total n = 1224). The prevalence was 21.9 per 100,000 overall and 1.6 per 100,000 when restricting to molecularly-confirmed XLHED cases. The most frequent age at time of XLHED diagnosis occurred between the ages of 11 and 18 years. Teeth abnormalities occurred in 79% of all cases and 52% of molecularly-confirmed cases as a primary clinical marker.ConclusionWe present the first ever population-based prevalence estimates of XLHED and suggest that the prevalence of XLHED may be higher than previously estimated. Diagnosis occurs most frequently during adolescence and teeth abnormalities were the most frequent clinical marker of XLHED.