rs1801260 — CLOCK 3111T>C (3'UTR)

Core circadian clock transcription factor variant affecting mRNA stability, associated with evening preference, delayed sleep onset, and shorter sleep duration

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CLOCK 3111T>C — Your Inner Night Owl Gene

The CLOCK gene (Circadian Locomotor Output Cycles Kaput) encodes the master transcription factor11 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)22 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 study33 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 site44 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 loop55 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 study66 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)77 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)88 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)99 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 ADHD1010 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.

Genotype Interpretations

What each possible genotype means for this variant.

AA Standard Circadian Normal

Normal CLOCK expression and typical circadian timing

With the AA genotype, the miR-182 binding site in the CLOCK 3'UTR is intact, allowing normal post-transcriptional regulation of CLOCK mRNA levels. Your circadian transcription-translation feedback loop operates with standard CLOCK protein abundance, and your intrinsic circadian period is not shifted by this particular variant.

In the Katzenberg et al. 1998 study, AA homozygotes had higher Horne-Ostberg scores on average (more morning-oriented) compared to minor allele carriers. In the Benedetti et al. 2007 actimetric study, AA individuals showed earlier sleep onset and longer total sleep time than C allele carriers.

In weight loss studies, AA homozygotes responded better to dietary interventions, losing more weight on both Mediterranean and low-fat diets compared to carriers of the minor allele.

AG Evening Tendency Intermediate

One copy of the evening-preference allele — mild circadian shift

With one copy of the variant allele, you have an intermediate level of CLOCK mRNA stabilization. The miR-182 binding site is disrupted on one chromosome but intact on the other, producing a moderate increase in CLOCK protein relative to AA homozygotes.

In the Benedetti et al. 2007 study, heterozygous carriers of the C allele showed an average 79-minute delay in sleep onset and 75 fewer minutes of sleep compared to T/T homozygotes (the study grouped all C carriers together). In the Garaulet et al. 2010 study, minor allele carriers (AG and GG combined) lost less weight on a Mediterranean diet intervention and were more likely to be short sleepers.

The Garcia-Rios et al. 2014 study found that minor allele carriers had a blunted improvement in insulin sensitivity on a low-fat diet compared to AA homozygotes, suggesting the circadian shift affects metabolic responses to dietary interventions.

GG Strong Evening Preference High

Two copies of the evening-preference allele — significant circadian delay

With two copies of the variant allele, both CLOCK 3'UTR copies have disrupted miR-182 binding sites, resulting in the highest CLOCK mRNA stability and protein levels among the three genotypes. This produces the most pronounced circadian phase delay.

GG homozygotes in the Garaulet et al. 2010 study showed the greatest difficulty with weight loss and the highest rate of short sleep duration. In the Garcia-Rios et al. 2014 study, minor allele homozygotes showed the weakest metabolic improvement on a low-fat diet, with significantly blunted insulin sensitivity gains compared to AA carriers.

An association with Parkinson's disease susceptibility was found in a Chinese population study (Lou et al. 2017, n = 620), where the CC genotype (GG on plus strand) was associated with increased PD risk, though this requires replication in other populations.

The frequency of short-time sleepers (6 hours or fewer per night) was significantly higher among minor allele homozygotes compared to non-carriers (59% vs 41%, P < 0.05), suggesting a real impact on habitual sleep duration.