ABSTRACT
Strong evidence exists that genetic predisposition and environmental
factors contribute to the development of asthma and other atopic diseases as suggested in Chapter 3 and a number of other sources (1-3). Epide-
miology has identified a number of environmental risk factors for asthma
and atopy in recent years but still, the presence of asthma in first degree
relatives of a child is the single most important risk factor for the develop-
ment of the disease (3). Thus, it seems that different environments may only
influence, trigger, or protect from a disorder, which is predominantly based
on an individual’s genetic susceptibility. In addition, gender and age effects
may modify the interaction between risk factors and genes. Due to these complex interactions, asthma is a truly multifactorial disorder in which
the effect of a single genetic factor may be hard to detect and to evaluate.
However, models testing environmental as well as genetic influences on the
occurrence of a disease over generations have been used in family studies to
disentangle genetics from environmental contributions. In asthma, allergic
rhinitis, or atopic eczema, these segregation analyses revealed a strong but
not exclusive genetic contribution (4-7). Instead of a Mendelian pattern of inheritance, mixed models of genetic and environmental influences gave the
best match with the observed distribution of asthma in extended families.
When asthma was studied in twins, genetics showed a much stronger impact
on disease development than did the environment. Based on these different
studies, heritability, the genetic contribution to the development of asthma,
was estimated to be between 60% and 80% (8,9).
