Background: A maternal line of inheritance regarding eczema has been described in several studies, whereasothers find associations to both a maternal as well as a paternal line of inheritance. When studying family historyof eczema symptoms, cohort studies including siblings are rare. Time point for assessing family eczema-historycould be of importance when studying the associations between family eczema-history and children with eczema,as parents with unaffected children may not recall mild symptoms in other siblings or their own disease history.We therefore aimed to study the associations between reported eczema in mother, father and siblings andreported eczema in index child where information on family history was collected at two different ages of indexchild.Methods: Parents/children participating in The Prevention of Allergy among Children in Trondheim (PACT) studywere given questionnaires on reported eczema symptoms in mother, father and siblings at 6 weeks and 1 year.When index child was 2 years of age, a detailed questionnaire on different health issues with emphasize ondifferent allergy related disorders were filled in.Results: Both maternal and paternal reports on eczema were significantly associated with eczema in index child.Reporting family eczema-history at 1 year (N = 3087), “eczema sibling only” [adjusted odds ratio (aOR) = 3.13 (2.27-4.33)] as well as all other family-groups containing siblings with eczema were strongly associated with eczema 2years. When family eczema-history was reported at 6 weeks (N = 2657), reporting of “eczema sibling only” was notassociated to reported eczema at 2 years in index child [aOR = 1.31 (0.77-2.23)].Conclusions: Having sibling(s) with eczema strengthened the associations between maternal and paternal reportson eczema with eczema in index child only when exposure was reported at 1 year. These findings indicate thatresults from questionnaires-based studies of family eczema-history depend on whether or not index child has yetdeveloped eczema.
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