The aim of this study was to estimate the relative influence of genetic and environmental factors on the aetiology of asthma.The classic twin study design was used to analyse data on self-reported asthma obtained by a questionnaire mailed to 34,076 individuals, aged 12±41 yrs and originating from the Danish Twin Register.The cumulative incidence of asthma was 6.2% in the pooled sample. The data showed a decreasing cumulative incidence with age for males, but no sex or zygosity difference was observed. Substantially higher concordance rates, odds ratios and correlations for asthma were estimated in the monozygotic than in the dizygotic twins. Using biometric modelling, a model including additive genetic and nonshared environmental effects provided the best overall fit to the data. According to this model, 73% of the variation in liability to asthma was explained by genetic factors. No sex difference or age-dependency in the magnitude of genetic effects was observed.The biometric analysis emphasized a major influence of genetic factors in the aetiology of asthma. However, a substantial part of the variation in liability to asthma is due to the impact of environmental factors specific to the individual. There is no evidence for a substantial impact of genetic dominance or the shared environment. Eur Respir J 1999; 13: 8±14. Exposure to altered or increased amounts of potentially harmful environmental factors may be a contributing factor to the observed increase in the prevalence of asthma that has been reported during recent decades. A change in susceptibility due to decreased host resistance caused by an altered biological response to environmental agents may be another explanation, whereas an increased genetic susceptibility due to a change in the genetic pool is unlikely to have occurred during the short period over which the increase in prevalence has been reported.The classic twin study comparing phenotypic similarity in monozygotic (MZ) and dizygotic (DZ) twins is a wellestablished and often used method to estimate the genetic and environmental influence on a trait. A few large-scale twin studies on asthma have been carried out in recent years. The largest study, including 13,888 Finnish twin pairs [1], was based on register linkage and the results underlined a major impact of environmental factors on the development of the disease. In contrast, questionnairebased studies have provided comparable results, emphasizing a major influence of genetic factors on the aetiology [2±4]. None of these twin studies found evidence for an impact of the shared (family) environment. However, other study designs have suggested that susceptibility to asthma may be determined early in life by environmental exposures such as passive smoking, especially maternal smoking [5], and exposure to indoor allergens [6±8], since they are frequent causes of allergy in children and associated with the development of asthma. These factors may be part of the common environment in childhood and adolescence, during which a majority of...

The susceptibility to develop atopic dermatitis can be attributed both to genetic and environmental causes. We estimated the relative impact of genetic and environmental factors in the etiology of atopic dermatitis in a population-based sample of twins. From the birth cohorts of 1953-1982 who were enrolled in The Danish Twin Registry, a total of 11,515 twin pairs were identified in a nationwide questionnaire survey. Subjects were classified as atopic dermatitis cases when responding affirmatively to the question, "Do you have, or have you ever had, eczema in the folds of your elbows or knees?" Latent factor models of genetic and environmental influences were fitted to the observed data using maximum likelihood methods. The overall lifetime prevalence of atopic dermatitis was 7.3%. A cotwin of an affected identical twin had a sevenfold increased risk of atopic dermatitis compared with a threefold increased risk among cotwins of an affected fraternal twin, relative to the general population. Genes accounted for 82% and nonshared environmental factors accounted for 18% of the individual susceptibility to develop atopic dermatitis. The same genes contributed to the susceptibility to atopic dermatitis both in male and female patients (p = 0.98). The estimates were adjusted for age. The susceptibility to develop atopic dermatitis is attributable to mainly genetic differences between people. However, differences in environmental exposures also are of importance.

This study does not support a role for selenium in protection against asthma, but effect modification and confounding cannot be ruled out.

No abstract

Studies from the UK and USA suggest that frequent use of paracetamol (acetaminophen) may increase the risk of asthma, but data across Europe are lacking.As part of a multicentric case-control study organised by the Global Allergy and Asthma European Network (GA 2 LEN), it was examined whether or not frequent paracetamol use is associated with adult asthma across Europe. The network compared 521 cases with a diagnosis of asthma and reporting of asthma symptoms within the last 12 months with 507 controls with no diagnosis of asthma and no asthmatic symptoms within the last 12 months across 12 European centres. All cases and controls were selected from the same population, defined by age (20-45 yrs) and place of residence. In a random effects meta-analysis, weekly use of paracetamol, compared with less frequent use, was strongly positively associated with asthma after controlling for confounders. There was no evidence for heterogeneity across centres. No association was seen between use of other analgesics and asthma.These data add to the increasing and consistent epidemiological evidence implicating frequent paracetamol use in asthma in diverse populations.