Parental and comorbid migraine in individuals with bipolar disorder: A nationwide register study

- A nationwide study on familial clustering of bipolar disorder (BD) and migraine.
- We also examined BD and comorbid migraine, adjusting for parental BD and migraine.
- BD was associated with both parental and comorbid migraine.
- Our results indicate that parental migraine is a risk factor for offspring BD.
- Non-genetic factors are likely to influence BD and migraine comorbidity.

BackgroundGenetic studies imply a shared genetic etiology between bipolar disorder (BD) and migraine. Epidemiological studies have demonstrated elevated comorbidity between these disorders, but haven't controlled for parental psychopathology. No previous nationally representative studies exist on familial clustering of BD and migraine. This study examines the association between parental and comorbid migraine and BD, controlling for potential confounders.MethodsWe identified 1861 cases aged ≤25 years, 3643 matched controls, and their parents from Finnish national registers. Conditional logistic regression was used to calculate odds ratios (ORs) with 95% confidence intervals (CIs) and two-sided significance limits of p<0.05.ResultsParental migraine, controlling for parental BD, was associated with offspring BD diagnosed at age ≥18 years (OR 1.52, 95%CI: 1.08-2.14). Associations between BD and comorbid migraine persisted following adjustment for parental BD and parental migraine in all subjects (OR=2.46, 95% CI: 1.76-3.42), both age groups of BD-diagnosis (<18 years,≥18 years) and both sexes.LimitationsThe diagnoses were register-based, not directly ascertained.ConclusionsThis study indicates that parental migraine, even in the absence of parental BD, is a risk factor for offspring BD. Thus, a genetic link between BD and migraine could potentially explain some of the elevated comorbidity between these disorders. However, BD shows a stronger association with comorbid migraine than with parental migraine, suggesting that much of the elevated comorbidity is related to non-genetic factors. Increased understanding of mechanisms underlying the comorbidity of BD and migraine is important since it is associated with poorer health-related outcomes compared with BD alone.