Familial risks for migraine and other headaches among siblings based on hospitalizations in Sweden.

Migraine and other headaches are common disabling conditions, reducing the quality of life in the affected individuals. The unambiguous definition of familial risk for subtypes of migraine and other headaches will advance the search for the heritable causes of these conditions and their underlying mechanisms. We aim at defining familial risks for siblings to be hospitalized because of migraine or other headaches. An ad hoc migraine database was constructed by linking the Multigeneration Register on 0- to 69-year-old siblings to the Hospital Discharge Register for data on migraines of all hospitalized patients in Sweden from years 1987 to 2001. Standardized incidence ratios (SIRs) were calculated for affected sibling pairs by comparison with those whose siblings had no migraine. Among a total of 14,123 hospitalized patients, 205 affected siblings were identified, with a familial SIR of 2.84. SIRs for migraine with and without aura were 3.08 and 2.67, respectively. The highest familial risk of 3.71 was noted for unspecified migraine. The risk tended to be higher for concordant (both siblings sharing the migraine subtype, ranging from 4.0 to 6.0) than discordant subtypes, but even many discordant SIRs were significant. The SIR for spouse correlation was 1.14 for husbands and 1.22 for wives, far from being significant. All subtypes of hospitalized migraines and other headaches show an increased familial risk, at least in specific age groups. The different subtypes appear to share susceptibility, which may imply common disease mechanisms.