title: Association between the melanopsin gene polymorphism OPN4*Ile394Thr and sleep/wake timing in Japanese university students.
abstract: BACKGROUND
  In our previous studies, we found that the Ile394Thr SNP in the melanopsin gene (OPN4) was functionally associated with the pupillary light reflex. This indicates the possibility that OPN4*Ile394Thr is associated with other non-image forming responses. The aim of this study was therefore to determine whether OPN4*Ile394Thr is associated with sleep/wake timing.
  
  
  METHODS
  A total of 348 healthy Japanese university students participated in this study. Scalp hair was used to genotype the Ile394Thr SNP of OPN4. Sleep habits, including bedtime, wake time and sleep duration, were assessed separately for weekdays and weekends. A total of 328 samples, including 223 samples with TT genotype, 91 with TC genotype and 14 with CC genotype, were used for statistical analysis. No significant difference in age or male/female distribution was found among the three genotype groups.
  
  
  RESULTS
  There was no significant difference in circadian preference among the genotype groups. During weekdays, bedtime, wake time and midpoint of sleep for CC subjects were significantly later than those for TT and TC subjects. However, there was no difference between TT and TC subjects in any of their sleep habits. During weekends, bedtime of CC subjects was significantly later than those of TT and TC subjects, and the midpoint of sleep of CC subjects was significantly later than that of TC subjects.
  
  
  CONCLUSIONS
  Our findings demonstrated that OPN4*Ile394Thr is associated with sleep/wake timing. We also found that the sleep/wake timing of subjects with the CC genotype was later than that of subjects with the TT or TC genotype.
authors.forename: Sang-Il
authors.initials: SI
authors.lastname: Lee
authors.forename: Akiko
authors.initials: A
authors.lastname: Hida
authors.forename: Shingo
authors.initials: S
authors.lastname: Kitamura
authors.forename: Kazuo
authors.initials: K
authors.lastname: Mishima
authors.affiliation: Department of Human Science, Faculty of Design, Kyushu University, 4-9-1 Shiobaru, Minami-ku, Fukuoka 815-8540, Japan. higu-s@design.kyushu-u.ac.jp.
authors.forename: Shigekazu
authors.initials: S
authors.lastname: Higuchi
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D007564:Japan; D008297:Male; D020641:Polymorphism, Single Nucleotide / Q000235:genetics*; D017299:Rod Opsins / Q000235:genetics*; D012890:Sleep / Q000235:genetics* / Q000502:physiology*; D013334:Students / Q000706:statistics & numerical data*; D011795:Surveys and Questionnaires; D014495:Universities; D014851:Wakefulness / Q000235:genetics / Q000502:physiology; D055815:Young Adult; D000099210:Melanopsin
chemical_list: D017299:Rod Opsins; D000099210:Melanopsin