"We examined the co-occurrence of migraine and endometriosis within the largest known collection
of families containing multiple women with surgically confirmed endometriosis and in an
independent sample of 815 monozygotic and 457 dizygotic female twin pairs. Within the
endometriosis families, a significantly increased risk of migrainous headache was observed in women
with endometriosis compared to women without endometriosis (odds ratio [OR] 1.57, 95%
confidence interval [CI]: 1.12–2.21, P = 0.009). Bivariate heritability analyses indicated no evidence
for common environmental factors influencing either migraine or endometriosis but significant
genetic components for both traits, with heritability estimates of 69 and 49%, respectively.
Importantly, a significant additive genetic correlation (rG = 0.27, 95% CI: 0.06–0.47) and bivariate
heritability (h2 = 0.17, 95% CI: 0.08–0.27) was observed between migraine and endometriosis.
Controlling for the personality trait neuroticism made little impact on this association. These results
confirm the previously reported comorbidity between migraine and endometriosis and indicate
common genetic influences completely explain their co-occurrence within individuals. Given
pharmacological treatments for endometriosis typically target hormonal pathways and a number of
findings provide support for a relationship between hormonal variations and migraine, hormonerelated
genes and pathways are highly plausible candidates for both migraine and endometriosis.
Therefore, taking into account the status of both migraine and endometriosis may provide a novel
opportunity to identify the genes underlying them. Finally, we propose that the analysis of such
genetically correlated comorbid traits can increase power to detect genetic risk loci through the use
of more specific, homogenous and heritable phenotypes.
In summary, these results confirm the previously reported comorbidity between migraine and
endometriosis and indicate common genetic influences completely underlie their cooccurrence
within individuals. Therefore, to improve the physical health and emotional wellbeing
of many women—via improved treatment and pain relief—we suggest the presence of
migraine be investigated in women with endometriosis and vice versa. Additionally, our data
indicate comorbid migraine and endometriosis represents a subset of individuals with unique
genetic effects and may therefore provide a novel opportunity to identify the genes underlying
them. Consequently, we propose that the analysis of such genetically correlated comorbid traits
can increase power to detect genetic risk loci through the use of more specific, homogenous
and heritable phenotypes. Also, the identification of genetically correlated comorbid traits has
particular relevance to the currently popular genome-wide association (GWA) paradigm by
providing a tangible means to substantially improve the efficient use of both existing and future
GWA data. For example, in addition to the primary association analysis of GWA data to the
phenotype for which it was ascertained, secondary analyses may be performed for genetically
correlated comorbid traits. Furthermore, examination of comorbid/non-comorbid cases (and
controls) provides a unique opportunity to knowingly stratify according to genetic
homogeneity." http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2730957/pdf/nihms104887.pdf
