Heritability of migraine as a function of definition

The objective was to examine the main genetic and environmental architecture of migraine in the Screening Across Lifetime of Twin (SALT) Study as a function of definition. We performed a quantitative genetic study of the Swedish population and a total of 12,095 twin pairs aged 41–64 years were interviewed on the telephone by trained lay personnel using a structured questionnaire. Lifetime assessment of recurrent headache and two measures of migraine were obtained, diagnosis in line with the 1988 International Headache Society criteria and self-report. The lifetime prevalence was 10.3% for diagnosed and 21.4% for self-reported migraine. Among diagnosed cases 82.3% self-reported migraine. Among self-ascertained cases, 60.3% did not fulfil diagnostic criteria, and one third had not had recurrent headache. In multivariate analyses, genetic influences were common to diagnosed and self-reported migraine (42%) and specific to self-report migraine (11%). In univariate analyses, heritability was stable (52%) when “false positives” were removed from the case definition (diagnosed or self-reported migraine) and decreased the prevalence from 23 to 16% but dropped (from 52 to 38%) when “false negatives” were removed and decreased the prevalence from 23 to 17%. A relationship between the definition and the heritability of migraine was demonstrated and phenotypes of clinical and aetiologic relevance were disclosed.