CHRNA5 and cyclic hematopoiesis: About 80% of patients with cluster headache (CH) have a history of cigarette smoking[1]; a common genetic basis between CH and smoking has been suggested by the identification of a gene cluster on chromosome 15q25, encoding for neuronal acetylcholine receptor subunits α3, α5 and β4 (CHRNA5-CHRNA3-CHRNB4).