Characterisation of migraine prevalence, heritability and symptom phenotypes in the Norfolk Island population

Abstract

Norfolk Island is a small volcanic land mass, roughly eight kilometres long by five kilometres wide. The island is located in the South Pacific Ocean along the Norfolk Ridge approximately 1,500km southeast of Brisbane, Australia. The population is a self governing territory of Australia, settled in 1856 by Pitcairn Islander's descended from a limited number (<20) of English Bounty mutineer and Tahitian founders. To this day, approximately 80% of the permanent adult residents inhabiting Norfolk possess ancestral lineages to the original population founders. This community is characterised by admixture and geographical isolation. Previous epidemiological and genetic studies of cardiovascular risk traits and linkage disequilibrium suggest that the Norfolk population may be of particular use in investigating complex multifactorial disorders, including migraine. To characterise migraine in the Norfolk population, we have employed both International Headache Society (IHS) diagnostic criterion and Latent Class Analysis (LCA), a statistical method that identifies groupings of cases in multivariate categorical data. Research has particularly focussed on 377 related individuals who are informative for linkage studies. These individuals are a subset of the total cohort recruited during the 2000 Norfolk Island Health Study. Demographic investigations have identified a high prevalence of migraine compared to estimates reported in the general Caucasian population (approximately 12%). Approximately 23.6% individuals have been diagnosed in accordance with IHS guidelines. Furthermore, as is typically observed in Western populations migraine prevalence displays an unequal sex-specific distribution, with a higher proportion of affected female sufferers observed in an approximate 3 to 1 ratio. The most frequently reported migraine symptom phenotypes include attack duration, attack frequency, pulsating quality of the headache and light sensitivity (photophobia). A significant genetic component to migraine is evident in this population, with heritability estimates of 42% and 52% for IHS and LCA derived phenotypes, respectively. Given the unique structure of this population, elevated prevalence, increased preponderance of affected females and evidence of a significant genetic component (p<0.05), this population should be very useful for molecular studies to localise potential susceptibility genes.