rs12736689 — RGS16

Intronic/regulatory variant near RGS16 that is the strongest single-locus morningness GWAS hit (P=7.0×10⁻¹⁸); the C allele (~4% global frequency) is associated with earlier chronotype via RGS16-mediated cAMP gating in the suprachiasmatic nucleus

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RGS16 and the Morningness Signal — The Strongest Chronotype Locus in Human Genetics

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 timing, hormone release, and metabolism. Keeping those neurons synchronized — not just cycling individually but entraining as a coherent population — requires molecular conductors. One of the most important is RGS1622 RGS16
Regulator of G-protein Signaling 16; accelerates inactivation of Gαi/o subunits, terminating cAMP signaling pulses and creating a rhythmic window for intercellular synchrony in the SCN.

The variant rs12736689 sits approximately 20 kilobases downstream of the RGS16 gene, in a regulatory region that influences how much RGS16 protein the SCN produces. The C allele — rare at roughly 4% globally — is associated with the strongest morningness signal ever detected in human genetics. Out of hundreds of thousands of genetic variants tested in three independent studies totalling nearly a million people, this single locus has emerged at the top of the chronotype ranking every time.

The Mechanism

RGS16 controls chronotype 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 and synchronize the distributed clock network rhythms within the SCN. RGS16 protein levels themselves cycle over the 24-hour day, creating a timed window during which cAMP can accumulate. This rhythmic cAMP pulse synchronizes the dorsomedial SCN (which drives peripheral body-clock timing) with the ventrolateral SCN (which receives 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 and the behavioral circadian period lengthens. A longer internal period means the clock runs slow relative to the 24-hour day — the animal drifts toward later and later timing, the mouse equivalent of an extreme evening chronotype.

The rs12736689 C allele is in strong linkage disequilibrium55 linkage disequilibrium
LD (r²=0.89): the two variants are inherited together so frequently that knowing one allele predicts the other with ~89% accuracy (r²=0.89) with rs1144566, a missense variant (H137R) in the RGS16 coding sequence. The combined evidence suggests that the regulatory and structural variants at this locus jointly modulate RGS16 activity in the SCN, with higher activity corresponding to tighter cAMP gating and a faster, morning-biased clock.

The Evidence

The RGS16 locus is the most robustly replicated single locus in human chronotype genetics, having emerged independently in three large-scale GWAS using different populations and study designs.

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 identified rs12736689 as the top hit in 89,283 23andMe participants, with the T allele (non-morningness) showing OR 0.74 (95% CI 0.69–0.79) at P=7.0×10⁻¹⁸ — meaning the C allele confers approximately 1.35-fold higher odds of being a morning person per allele. Seven of the 15 significant loci clustered near established circadian genes, and RGS16 stood apart as the most significant of all.

Jones et al. (2016)77 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 independently identified the same RGS16 locus (lead SNP rs516134, in high LD with rs12736689) as the top chronotype hit in the UK Biobank, with OR 1.21 for the morningness allele at P=3×10⁻¹².

The definitive meta-analytic confirmation came from Jones et al. (2019)88 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, expanding the chronotype locus catalog to 351 genome-wide significant loci in 697,828 participants. The RGS16 locus remained the top hit. Mendelian randomization in this study established that the genetic component of morningness causally associates with better mental health outcomes — likely because earlier chronotype aligns more closely with typical daylight-hour social and work schedules.

Practical Implications

For TT homozygotes (the large majority), circadian timing sits at the population average — slightly toward the evening end of the spectrum relative to C allele carriers, but solidly typical. Environmental factors (morning light, meal timing, consistent schedule) are the primary levers for shaping rhythm.

For carriers of one or two C alleles, the RGS16 mechanism shifts the clock toward earlier timing. The practical benefit — alignment with conventional work schedules and better morning alertness — is real but modest at this single locus. The main risk is the rigid early clock: evening social or professional demands can conflict acutely with a biologically advanced sleep phase, and C allele carriers typically find it harder to stay up late without next-day consequences.

Interactions

rs12736689 and rs516134 both tag the same RGS16 regulatory region (r² ~0.89 with rs1144566). Carriers with other morningness variants — in CLOCK (rs1801260), PER3 (rs5751876), PER2 (rs55694368), or the VIP signaling gene (rs9479402) — may experience additive phase advances. Evening-allele carriers at multiple circadian loci show the greatest benefit from structured morning-light and meal-timing interventions to advance their clock.

Genotype Interpretations

What each possible genotype means for this variant.

TT Standard Circadian Timing Normal

Common genotype — no RGS16 morningness alleles

The TT genotype represents the population-major state at this regulatory locus. The RGS16 gene encodes a protein that gates cAMP signaling in the suprachiasmatic nucleus, synchronizing the dorsomedial and ventrolateral SCN subdivisions that coordinate the master body clock. Without the C allele's regulatory influence, RGS16 expression at this locus operates at the baseline level found in most of the population.

In the Hu et al. 2016 GWAS, TT carriers (B allele homozygotes) served as the reference group against which the morningness effect of the C allele was measured. In the Jones et al. 2019 mega-GWAS of 697,828 individuals, the cumulative effect of morningness alleles across all 351 loci shifts sleep midpoint by approximately 25 minutes between the top and bottom deciles of the polygenic score — the RGS16 locus is the largest single contributor but accounts for a modest fraction of this total shift.

CC Strong Morning Preference Beneficial

Two morningness alleles — strong early-chronotype genetics at RGS16

Carrying two C alleles at rs12736689 maximizes the regulatory influence on RGS16 expression at this locus, producing the strongest genetic push toward morningness from this variant. The biological mechanism — tighter circadian cAMP gating in the SCN via higher RGS16 activity — corresponds to a clock that entrains toward the earlier end of the timing distribution.

In Hu et al. 2016, the per-allele OR of ~1.35 for morningness is additive, giving CC homozygotes approximately OR 1.35² ≈ 1.82-fold higher odds of being a morning person compared to TT homozygotes. The 2019 Jones mega-GWAS of 697,828 individuals showed that carriers of many morningness alleles across 351 loci wake approximately 25 minutes earlier than those with the fewest morningness alleles; this locus is the single largest contributor to that polygenic effect.

The primary practical challenge for CC carriers is mismatch with late-evening social or professional schedules. Because the clock is strongly set to an early phase, it resists flexing to later timing, making late nights feel disproportionately costly the next morning.

CT Mild Morning Tendency Intermediate

One morningness allele — mild morning preference from RGS16

The C allele is thought to increase transcriptional activity at this RGS16 regulatory region, supporting higher RGS16 protein levels in the SCN. Higher RGS16 activity tightens the daily cAMP gating window, slightly shortening the effective circadian period — the molecular hallmark of an earlier-shifted clock.

In Hu et al. 2016, the per-allele effect was OR 0.74 for the non-morningness T allele, equivalent to OR ~1.35 per C allele for morningness. For the CT heterozygote, the relative odds of being a morning person are approximately 1.35-fold higher than TT. The effect is meaningful but modest; chronotype is highly polygenic and the environment — especially light timing — substantially modulates the genetic predisposition.

The 2019 Jones mega-GWAS established via Mendelian randomization that genetic morningness is causally associated with better mental health outcomes, likely through better circadian alignment with typical social and daylight schedules.