Association study of a variable-number tandem repeat polymorphism in the clock gene PERIOD3 and chronotype in Norwegian university students.
Level 4 - case-series / case-control
Cross-sectional genetic association study
PubMed 21919721 · doi:10.3109/07420528.2011.607375
What was done
Genotyped 432 healthy Norwegian university students for the 4-repeat and 5-repeat alleles of the variable-number tandem repeat (VNTR) polymorphism in the PERIOD3 (PER3) clock gene. Subjective diurnal preference (chronotype) was assessed using the Horne-Östberg Morningness-Eveningness Questionnaire (MEQ) and the Preferences Scale (PS).
What was found
The genotype distribution was 192 (4-4), 191 (4-5), and 49 (5-5). Despite an estimated 75% statistical power to detect an association of the 4-allele with preference for morningness or eveningness, the authors found no association between the PER3 clock gene polymorphism and chronotype (no numerical effect sizes or p-values reported in abstract).
Why it matters
The study fails to replicate previous reports linking the PER3 VNTR polymorphism to diurnal preference, suggesting that PER3 is not a robust standalone determinant of morningness or eveningness in young adults.
Limits
Statistical power was limited (estimated at 75%). The study evaluated a restricted, homogeneous sample of Norwegian university students. Chronotype was determined solely via subjective questionnaires without physiological circadian phase markers (such as core body temperature or melatonin).
Cited by
- contradicts Chronotypes (early bird vs. night owl) are genetically determined by a single nucleotide polymorphism in the PER3 genomic region.