CLOCK 3111T>C — Your Inner Night Owl Gene
The CLOCK gene (Circadian Locomotor Output Cycles Kaput) encodes the master
transcription factor | A protein that binds to DNA and activates the expression of other genes, in this case driving the ~24-hour circadian rhythm
at the heart of the mammalian circadian clock. Working with its partner BMAL1,
the CLOCK protein drives rhythmic expression of thousands of genes that
govern sleep-wake cycles, hormone secretion, metabolism, and body temperature.
The rs1801260 variant — commonly called 3111T>C using the coding strand
notation — sits in the
3' untranslated region (3'UTR) | The section of mRNA after the stop codon that doesn't code for protein but regulates mRNA stability, localization, and translation efficiency
of CLOCK mRNA, where it affects how long the messenger RNA persists in the
cell before being degraded.
This was the first human clock gene polymorphism linked to chronotype,
identified in a
landmark 1998 study | Katzenberg D et al. A CLOCK polymorphism associated with human diurnal preference. Sleep, 1998
at Stanford. Carriers of the minor allele scored significantly lower on the
Horne-Ostberg morningness-eveningness questionnaire, indicating a shift
toward evening preference that was independent of age, sex, and ethnicity.
The Mechanism
The rs1801260 variant falls within a
miR-182 binding site | MicroRNA-182 binds to the 3'UTR of CLOCK mRNA and promotes its degradation; the variant allele disrupts this binding
in the CLOCK 3'UTR. The minor allele (G on plus strand, C in coding strand
notation) disrupts this microRNA interaction site, resulting in increased
CLOCK mRNA stability. Cell-based studies using mouse embryonic fibroblasts
transfected with the rs1801260 construct showed that the variant allele
produces significantly higher levels of CLOCK and downstream Per2 mRNA.
Higher CLOCK protein levels extend the active phase of the
transcription-translation feedback loop | The core circadian mechanism: CLOCK/BMAL1 activate PER and CRY genes, whose proteins then inhibit CLOCK/BMAL1, creating a ~24-hour oscillation
that defines circadian period length. This molecular shift manifests
behaviorally as delayed sleep onset, higher evening activity, and a
preference for later bed and wake times.
The Evidence
The
original Katzenberg study | Katzenberg D et al. A CLOCK polymorphism associated with human diurnal preference. Sleep, 1998
genotyped 410 adults from a population-based sample and found that C allele
carriers had significantly lower Horne-Ostberg scores (shifted toward
eveningness), independent of age, sex, and ethnic background.
Benedetti et al. (2007) | Benedetti F et al. Actimetric evidence that CLOCK 3111 T/C SNP influences sleep and activity patterns in patients affected by bipolar depression. Am J Med Genet B Neuropsychiatr Genet, 2007
provided objective actimetric data in 39 bipolar depressed inpatients,
showing that C allele carriers had 79 minutes later sleep onset and 75 fewer
minutes of total sleep compared to T/T homozygotes, with higher evening
activity levels — all despite similar depression severity.
The metabolic consequences of this chronotype shift have been well
documented.
Garaulet et al. (2010) | Garaulet M et al. CLOCK gene is implicated in weight reduction in obese patients participating in a dietary programme based on the Mediterranean diet. Int J Obes, 2010
studied 1,100 overweight and obese subjects and found that minor allele
carriers lost significantly less weight during a Mediterranean diet
intervention (P = 0.008), with more carriers being short sleepers
(59% vs 41%, P < 0.05).
Garcia-Rios et al. (2014) | Garcia-Rios A et al. Beneficial effect of CLOCK gene polymorphism rs1801260 in combination with low-fat diet on insulin metabolism in metabolic syndrome. Chronobiol Int, 2014
found significant gene-diet interactions in 475 metabolic syndrome patients:
after 12 months on a low-fat diet, major allele homozygotes (AA) showed
lower insulin and HOMA-IR, while minor allele carriers did not improve as
much (interaction P = 0.009 for insulin, P = 0.014 for HOMA-IR).
An
association with adult ADHD | Kissling C et al. A polymorphism at the 3'-untranslated region of the CLOCK gene is associated with adult attention-deficit hyperactivity disorder. Am J Med Genet B, 2008
was found in 143 subjects (P < 0.001), consistent with the known circadian
rhythm disruption in ADHD.
It is important to note that large genome-wide association studies of
chronotype have not consistently replicated the rs1801260 signal. This may
reflect the modest effect size of any single variant and the polygenic
nature of chronotype, where hundreds of variants each contribute small
effects.
Practical Implications
The CLOCK 3111C allele is not a sleep disorder — it is a common variant
that tilts circadian preference toward eveningness. The practical relevance
is in recognizing this tendency and structuring daily routines to work with
it rather than against it.
For weight management, the evidence suggests that minor allele carriers may
benefit from paying particular attention to meal timing, eating the main
meal earlier in the day, and avoiding late-night eating. The combination
of evening preference and shorter sleep creates a metabolic environment
that favors weight gain through altered ghrelin, GLP-1, and insulin
dynamics.
Light exposure is the strongest environmental cue for circadian
entrainment. Morning bright light exposure (10,000 lux for 20-30 minutes
upon waking) can help shift the circadian phase earlier, partially
counteracting the genetic evening tendency. Conversely, evening blue light
from screens further delays sleep onset in already evening-shifted
individuals.
Interactions
The CLOCK 3111C allele interacts with SIRT1 variants to produce additive
effects on evening preference and weight loss resistance. Garaulet et al.
(2012) showed that carriers of minor alleles at both SIRT1 (rs1467568) and
CLOCK (rs1801260) had the strongest evening preference and greatest
resistance to weight loss in a behavioral obesity treatment.
CLOCK also interacts functionally with PER2 and PER3 — the period genes
that form the negative limb of the circadian feedback loop. While specific
gene-gene interaction studies for rs1801260 with PER variants are limited,
the biological pathway logic is strong: increased CLOCK expression drives
higher PER/CRY production, and variants in PER genes that alter this
response could compound the circadian shift.
All genotypes
Normal CLOCK expression and typical circadian timing
You have two copies of the common A allele (T on the coding strand). Your CLOCK mRNA is regulated normally by miR-182, resulting in standard circadian clock protein levels. You have no genetically driven shift toward evening preference from this variant. About 53% of people globally share this genotype, making it the most common. In East Asian populations, this genotype is especially prevalent at around 76%.
One copy of the evening-preference allele — mild circadian shift
You carry one copy of the G allele (C on the coding strand), which increases CLOCK mRNA stability and protein levels. This shifts your circadian preference mildly toward eveningness. You may naturally tend toward later bedtimes and find mornings more difficult than AA homozygotes. About 39% of people globally share this genotype. It is very common and represents a subtle tendency, not a disorder.
Two copies of the evening-preference allele — significant circadian delay
You carry two copies of the G allele (C on the coding strand), maximizing the increase in CLOCK mRNA stability and protein levels. You likely have a noticeable preference for evening activity and later bedtimes, and you may find it particularly difficult to function well in early-morning schedules. About 8% of people globally share this genotype. It is less common overall but reaches higher frequencies in South Asian populations where the minor allele is more prevalent.