Genetic factors in nickel allergy evaluated in a population-based female twin sample.

Environmental exposures are important for development of allergic contact dermatitis, but genetic factors have been proposed to be of additional importance for contact sensitization. Recently genetic factors were shown to be of significance for hand eczema. In this study, a sample of twins recruited on the basis of hand eczema has been evaluated with respect to influence of genetic factors on development of nickel sensitization. A total of 1076 individual twins were patch tested and underwent clinical examination, and in the final genetic statistical analysis 630 females were available, of which 146 had a positive patch test to nickel. The aggregation of nickel allergy among twin pairs was measured by the casewise concordance and the twin odds ratio. The twin odds ratio were adjusted for effects of risk factors known to be associated with nickel allergy, namely, wet work, atopic dermatitis, and self-reported hand eczema. There was a small tendency for larger odds ratio among monozygotic twins than among dizygotic twins, which was not statistically significant. As a result of the statistical analysis, it is concluded that allergic nickel contact dermatitis is mainly caused by environmental and only to a lesser degree genetic factors. The selection of twins on the basis of hand eczema may theoretically influence the prevalence of nickel allergy and concordance estimates, which should be considered before extrapolating the data to a random population-based twin sample.