What this means

PER3 is another core circadian-clock gene. Its best-known variant is a variable-number-tandem-repeat (VNTR) in exon 18 that exists as a 4- or 5-repeat allele — the 5-repeat form is associated with morningness and slightly higher sleep pressure under deprivation. The VNTR doesn't appear on most SNP arrays, but rs10462020 sits nearby and partially tracks the haplotype. The associations are real but small, and like CLOCK this SNP nudges chronotype rather than reassigning it.

PER3 is another one of the core genes that runs your body's daily rhythm. The most-studied PER3 variant is a chunk of DNA that repeats either 4 or 5 times — the 5-repeat version is linked to being more of a morning person, and feeling more tired after a bad night's sleep. That variant doesn't show up on standard tests, so this looks at a nearby spot that partially tracks it. Like CLOCK, this gene nudges your chronotype a notch rather than reassigning it.

Caveats

• rs10462020 is a partial proxy for the PER3 VNTR — accuracy is imperfect.
• Effect sizes on chronotype are small.
• The most robust evidence is for differences in sleep deprivation response, not everyday chronotype.
• Chronotype is highly polygenic; this is one of many small contributors.

References

• Viola et al. — PER3 polymorphism predicts sleep structure and waking performance (Current Biology, 2007)
• Archer et al. — A length polymorphism in the circadian clock gene Per3 is linked to delayed sleep phase syndrome and extreme diurnal preference (Sleep, 2003)