Abstract
Dear Sir I read with extreme interest the paper from Rueda-Sánchez and Díaz-Martínez (1), in which trhey contrasted demographic factors and exposures associated with episodic migraine and chronic daily headache (CDH) in the Colombian population. From the many factors assessed, family history of CDH figured prominently. Among individuals with CDH, an astonishing 31.5% reported a history of daily headaches in their parents (contrasted with 9.8% in controls). Furthermore, 20.7% of the CDH sufferers reported CDH in their children, vs. 3.7% of controls. In individuals with migraine, CDH in the family was more common than in controls, and less common than in families of probands with CDH.
Because the paper is so dense, these findings may receive less attention than they should. It is well established that migraine aggregates within families (2–6) and that the rates of aggregation are higher in the families of migraineurs that are severely disabled (4, 7). However, aggregation of CDH had not been described to the best of my knowledge. Furthermore, the aggregation of CDH in the families of individuals with episodic migraine offers further support to migraine progression (episodic migraine evolving to CDH) (8). It is possible that, among individuals with migraine, presence of specific genes (e.g. pain progression genes) and/or common family exposure to exogenous factors (e.g. specific social or psychological stressors that affect the entire family) would predispose to CDH.
The findings from this study may also be relevant to studies designed to identify genes associated with CDH. A critical challenge in these types of studies is to identify families with a high genetic loading for disease. Using the high density approach, families with multiple affected individuals are sought (7). However, this strategy is often limited to a small number of relatively large and difficult to find families. An alternative strategy is to search for probands with CDH or high-severity migraine, or both, and to study their families.