rs516134 — RGS16 RGS16 chronotype variant

RGS16 — The Pacemaker Synchronizer That Sets Your Body Clock

Deep inside the hypothalamus, a cluster of roughly 20,000 neurons called the suprachiasmatic nucleus (SCN)¹¹ suprachiasmatic nucleus (SCN)
The brain's master circadian clock, located in the hypothalamus above the optic chiasm; it generates and coordinates ~24-hour biological rhythms throughout the body fires in near-perfect 24-hour cycles, orchestrating sleep, hormone release, and metabolism across every cell in the body. Keeping those neurons synchronized with each other — not just cycling individually — requires a molecular conductor. RGS16²² RGS16
Regulator of G-protein Signaling 16; a protein that accelerates the inactivation of G-protein alpha subunits, terminating cAMP signaling pulses is that conductor.

The rs516134 variant sits approximately 20 kilobases downstream of the RGS16 gene, in a regulatory region that influences how much RGS16 the SCN produces. Carriers of the C allele — the minor allele at this position — tend to wake earlier, feel alert sooner after rising, and perform best in the morning. This makes rs516134 the top replicated chronotype hit in human genetics, having emerged independently in three major genome-wide association studies spanning nearly 700,000 people.

The Mechanism

RGS16 exerts its circadian influence by gating cAMP³³ cAMP
Cyclic AMP (cyclic adenosine monophosphate), a second messenger that amplifies signals from G-protein-coupled receptors; in the SCN, timed cAMP pulses coordinate neuron-to-neuron communication production in the SCN. In the intact clock, RGS16 protein levels rise and fall over the 24-hour cycle, creating a time window each day during which cAMP can accumulate. This rhythmic cAMP pulse synchronizes the dorsomedial SCN neurons (which drive the rest of the body) with the ventrolateral neurons (which receive light input from the retina).

Doi et al. (2011)⁴⁴ Doi et al. (2011)
Doi M et al. Circadian regulation of intracellular G-protein signalling mediates intercellular synchrony and rhythmicity in the suprachiasmatic nucleus. Nature Communications, 2011 showed that when RGS16 is deleted in mice, the circadian cAMP rhythm collapses entirely — and the behavioral circadian period lengthens. A longer internal period means the clock runs slow relative to the 24-hour day, causing the animal (and, by analogy, the human) to drift toward later and later timing — exactly the phenotype associated with low RGS16 activity.

The rs516134 C allele appears to support higher regulatory-region activity, boosting RGS16 expression, tightening cAMP gating in the SCN, and shortening the effective period toward a morning-shifted chronotype. The molecular details of how the variant changes transcription factor binding at this regulatory element remain under active investigation.

The Evidence

The RGS16 locus has the distinction of being the most strongly replicated single locus in human chronotype genetics. Three independent large-scale GWAS, each using different populations and methods, have all converged on this region.

Jones et al. (2016)⁵⁵ Jones et al. (2016)
Jones SE et al. Genome-Wide Association Analyses in 128,266 Individuals Identifies New Morningness and Sleep Duration Loci. PLoS Genetics, 2016 analyzed 128,266 UK Biobank participants and identified rs516134 as the lead SNP at the RGS16 locus, with the C allele conferring an odds ratio of 1.21 (95% CI 1.15–1.27) for morningness at P=3×10⁻¹².

Hu et al. (2016)⁶⁶ Hu et al. (2016)
Hu Y et al. GWAS of 89,283 individuals identifies genetic variants associated with self-reporting of being a morning person. Nature Communications, 2016 independently studied 89,283 23andMe participants and found the same locus — represented by the linked variant rs12736689 — as the single most significant chronotype hit at P=7×10⁻¹⁸. Seven of the 15 significant loci fell near known circadian genes, with RGS16 the strongest.

The definitive meta-analytic confirmation came from Jones et al. (2019)⁷⁷ Jones et al. (2019)
Jones SE et al. Genome-wide association analyses of chronotype in 697,828 individuals provides insights into circadian rhythms. Nature Communications, 2019, which expanded the catalog of chronotype loci from 24 to 351 in 697,828 individuals. The pathway analysis implicated cAMP signaling, circadian regulation, and retinal/hypothalamic expression — all converging on the biology explained by RGS16. Using Mendelian randomization, the study showed that being a morning person is causally associated with better mental health outcomes.

Practical Implications

For carriers of TT (the common genotype), circadian timing is close to the population average — not sharply morning or evening, but with a gentle evening lean compared to C allele carriers. The practical implication is awareness: your biological clock has no strong push toward morningness, so environmental factors (light exposure, meal timing, sleep scheduling) matter more in shaping your daily rhythm.

For carriers of one or two C alleles, the clock runs slightly faster, making it easier to wake early and fall asleep earlier. This is an advantage in most modern work schedules but can become a liability when evening social or professional demands conflict with an early-dimming internal clock. Evening light exposure and slightly later meal timing can extend alertness into the evening when needed.

Light therapy is the most evidence-based intervention for chronotype adjustment in either direction. Morning bright light (10,000 lux) reinforces early timing; evening blue-light reduction prevents unwanted advance for C allele carriers who want to stay up later.

Interactions

rs516134 acts within the same circadian feedback network as variants in CLOCK (rs1801260), PER3 (rs5751876), and the VIP receptor gene. These SNPs operate at different nodes of the circadian oscillator: CLOCK affects transcription factor stability, PER3 affects the negative feedback arm, and RGS16 affects intercellular synchrony via cAMP. Carriers of evening-tendency alleles at multiple loci may experience additive chronotype shifts beyond what any single SNP predicts.

The GPR176–Gz–RGS16 axis is also under investigation for its relationship to human chronotype variation more broadly (PMID 28502923), and several nominally associated variants upstream of RGS16 have been identified in the larger GWAS datasets that may refine the functional signal at this locus.