A genetic CLOCK variant associated with cluster headache causing increased mRNA levels

Cluster headache is characterized by recurrent unilateral headache attacks of severe intensity. One of the main features in a majority of patients is a striking rhythmicity of attacks. The CLOCK (Circadian Locomotor Output Cycles Kaput) gene encodes a transcription factor that serves as a basic driving force for circadian rhythm in humans and is therefore particularly interesting as a candidate gene for cluster headache.