Characterization by phenotype of families with atopic dermatitis.

The aetiology of atopic dermatitis is unknown, but is probably multifactorial, with interactions between several genetic and environmental factors. Twin studies indicate a strong genetic factor, but the susceptibility genes are unknown. This paper, describing the phenotypes of family material, forms part of a large genetic study seeking to identify susceptibility genes for atopic dermatitis by linkage analysis. We selected families with at least 2 siblings affected with atopic dermatitis (1,097 affected siblings who together form 650 affected sib pairs and 49 affected half-sib pairs). We established a phenotype database of information about the affected siblings and their relatives, in total 5,830 individuals. All siblings were diagnosed with atopic dermatitis and participated in a standardized interview covering aspects of atopy and atopic dermatitis. Of the affected siblings, 72% suffered or had suffered from asthma and/or allergic rhinoconjunctivitis and 74% had raised total and/or allergen-specific IgE serum levels. Seventeen percent of the siblings had been hospitalized for atopic dermatitis. Sixty-nine percent had 1 or both parents with atopic dermatitis. Among siblings with 1 parent with atopic dermatitis, 37% had a father with atopic dermatitis and 63% had a mother with atopic dermatitis, indicating maternal preponderance. Analysis of the occurrence of atopic dermatitis in relation to the birth order in the sibship shows an increased risk of atopic dermatitis in persons born early in a sibship. Although the families were selected for genetic sib-pair linkage analysis, we believe that this material is representative of atopic dermatitis families managed at hospitals in Stockholm.