title: Lack of association between cluster headache and PER3 clock gene polymorphism.
abstract: BACKGROUND
  Cluster headache (CH) is regarded as a chronobiological disorder. The hypothalamic biological clock may thus be involved in the pathophysiology, but few studies have actually investigated this in CH patients. A variable number tandem repeat (VNTR) polymorphism of the PER3 clock gene has been associated to preferred daily rhythm (chronotype) in several studies. We aimed to study the distribution of PER3 VNTR polymorphisms and chronotypes in a CH population.
  
  
  METHODS
  We used blood samples from a biobank of CH patients for genetic tests, and invited all tested patients to complete the Horne-Ostberg Morningness-eveningness Questionnaire (MEQ), the Pittsburgh sleep quality Index (PSQI) and the Shift Work Index. Genotypes were compared to a previously tested population of 432 healthy students.
  
  
  RESULTS
  One hundred forty nine patients were genotyped, and we found no difference in PER3 VNTR polymorphisms between patients and controls. Seventy-four patients completed the MEQ (54 men, 20 women, mean age 52.3 years ± 13.4), and chronotypes were as follows: 12 % morning-, 37 % intermediate-, and 51 % evening types. Compared with a previous Danish study of CH patients and controls, there were no difference in chronotype distribution. Sixty percent of patients were defined as bad sleepers (PSQI >5), and 51 % of patients currently employed were shift workers.
  
  
  CONCLUSIONS
  No association between CH, PER3 VNTR polymorphism and chronotype was found in this study.
authors.affiliation: Department of Neurology, Nordland Hospital Trust, 8092, Bodø, Norway. hkofte@gmail.com.
authors.forename: Hilde K
authors.initials: HK
authors.lastname: Ofte
authors.affiliation: Department of Neuroscience, Norwegian University of Science and Technology, Edvard Griegs gate 8, 7491, Trondheim, Norway. erling.tronvik@ntnu.no.|St.Olavs Hospital, Trondheim, Norway. erling.tronvik@ntnu.no.
authors.forename: Erling
authors.initials: E
authors.lastname: Tronvik
authors.affiliation: Department of Neurology, Nordland Hospital Trust, 8092, Bodø, Norway. karl.bjornar.alstadhaug@nlsh.no.|The Arctic University of Norway, Tromsø, Norway. karl.bjornar.alstadhaug@nlsh.no.
authors.forename: Karl B
authors.initials: KB
authors.lastname: Alstadhaug
mesh_terms: D000328:Adult; D000368:Aged; D002940:Circadian Rhythm / Q000235:genetics; D003027:Cluster Headache / Q000235:genetics*; D005260:Female; D056726:Genetic Association Studies; D020022:Genetic Predisposition to Disease; D005838:Genotype; D006801:Humans; D008297:Male; D008875:Middle Aged; D018598:Minisatellite Repeats; D056950:Period Circadian Proteins / Q000235:genetics*; D011110:Polymorphism, Genetic
chemical_list: C512644:PER3 protein, human; D056950:Period Circadian Proteins
keywords: Chronotype; Clock genes; Cluster headache; Horne-Ostberg Morningness eveningness questionnaire; PERIOD3; Shift work