Family studies

The progress in the treatment of diseases caused by infection and malnutrition has changed the disease spectrum in developed and developing countries. Environmental diseases are nowadays being out-numbered by others which are entirely or partly genetically determined such as atopic dermatitis (AD), which has become one of the most common diseases of childhood (Schultz Larsen et al., 1996). Since the classical and comprehensive study of Cooke and van der Veer in 1916 it has been known that allergy runs in families. They found that if one parent was allergic, then nearly 50% of the children likewise had allergy; if both parents were allergic, then so too were 75% of their offspring. After the discovery of transmission of antibodies (reagins) in the 1920s, the road was opened for the definition of atopy and the underlining of the relationship of atopic dermatitis to the atopic diathesis. That common genes rather than common family environment causes this familial aggregation has been substantiated by several extensive publications (Edgren, 1943; Schwartz, 1952; Schnyder, 1960), but controversy has existed about the mode of inheritance. All types of Mendelian framework have been suggested, but in the 1960s the available data strongly indicated atopy as being polygenic and multifactorially determined, which means that several genes (polygenic) as well as genetic and environmental factors (multifactorial) determine the expression of the disease (Arsdel & Motulsky, 1959; Leigh & Marley, 1967).