rs476828 — MC4R MC4R-region BMI variant

The MC4R Haplotype — A Third Window into Appetite Regulation

The melanocortin-4 receptor (MC4R) gene sits at the center of your brain's appetite control system. Located in the hypothalamus¹¹ hypothalamus
the brain region governing hunger, satiety, and energy balance, MC4R receives signals from leptin and melanocortin hormones to generate "stop eating" commands. The stretch of chromosome 18 roughly 188 kilobases downstream of MC4R contains a regulatory haplotype block — a cluster of variants inherited together — that controls how much MC4R your neurons produce. rs476828 sits within this block.

This SNP tags the same obesity-associated haplotype as the better-known rs17782313, the second strongest common obesity genetic signal in humans²² second strongest common obesity genetic signal in humans
after FTO rs9939609. In Europeans, rs476828 and rs17782313 are in perfect linkage disequilibrium³³ perfect linkage disequilibrium
r²=1 in the CEU HapMap sample, meaning the two variants are essentially interchangeable as markers for the same underlying haplotype. In African-ancestry populations the LD is weaker (r²=0.526), meaning rs476828 carries some independent information there. Together with rs12970134, these three variants form the risk haplotype C–C–A, which carries OR=1.796 for obesity.

The Mechanism

rs476828 is an intergenic variant in a regulatory element⁴⁴ regulatory element
a stretch of DNA that controls gene transcription without encoding protein itself that modulates MC4R expression in hypothalamic neurons. The full signaling chain works as follows: fat cells secrete leptin⁵⁵ leptin
a hormone that reports energy stores to the brain, which activates POMC neurons⁶⁶ POMC neurons
proopiomelanocortin neurons in the arcuate nucleus that generate appetite-suppressing signals, which release alpha-melanocyte stimulating hormone (α-MSH), which binds MC4R. When MC4R fires, it suppresses appetite and increases energy expenditure. When regulatory variants reduce MC4R expression, this entire cascade is weakened — fewer receptors means quieter "stop eating" signals and reduced metabolic drive.

The C allele of rs476828 tags a haplotype associated with reduced MC4R promoter activity. Epigenetic studies⁷⁷ Epigenetic studies
MeQTL analyses examining DNA methylation quantitative trait loci show that this regulatory block is associated with increased MC4R promoter methylation, further suppressing expression. The net result is a hypothalamic satiety circuit that requires stronger signals to fire — meaning larger portions before fullness registers, and a higher baseline appetite drive.

The Evidence

The original landmark GWAS⁸⁸ landmark GWAS
Loos et al., Nature Genetics 2008, n=16,876 discovery + 60,352 replication identified this MC4R-region signal as the second strongest common BMI locus in humans. Per C allele, adults showed a 0.05 Z-score BMI increase (p=2.8×10⁻¹⁵); children aged 7–11 showed a larger 0.13 Z-score effect (p=1.5×10⁻⁸), and severe childhood obesity odds reached OR=1.30 (p=8.0×10⁻¹¹). rs476828 was directly studied in a childhood obesity cohort⁹⁹ childhood obesity cohort
Grant et al., 728 obese European American children and 3,960 controls and yielded OR=1.145 (p=0.042), consistent with its role as a perfect proxy for rs17782313 in European-ancestry individuals.

A 2020 haplotype study¹⁰¹⁰ 2020 haplotype study
Wei et al., Mol Med, 1,836 Chinese participants examined rs476828 directly and found the C allele significantly elevated in obesity cases versus controls (17.1% vs 10.9%, p<0.001), with a dominant-model OR of 1.585 (95% CI=1.176–2.136). The full C–C–A haplotype across rs17782313, rs476828, and rs12970134 yielded OR=1.796 (95% CI=1.447–2.229), illustrating that these three markers collectively tag a single high-risk regulatory configuration.

A prospective cohort study in 5,724 women¹¹¹¹ prospective cohort study in 5,724 women
Qi et al., Hum Mol Genet 2008 found that this MC4R locus (tagged by rs17782313) was associated with higher total energy and dietary fat intake, greater 10-year BMI gain, and 14% increased type 2 diabetes risk per C allele after BMI adjustment — indicating effects on metabolic regulation beyond adiposity alone.

A sex-specific layer was uncovered by neuroimaging in 284 adults¹²¹² neuroimaging in 284 adults
Horstmann et al., PLoS One 2013: female homozygous CC carriers showed increased gray matter volume in the right amygdala, hippocampus, and orbitofrontal cortex — regions encoding emotional memory and food reward — as well as significantly elevated disinhibition and emotional eating scores. These effects were absent in men, suggesting the MC4R regulatory haplotype has sex-specific impacts on the neural circuits governing food motivation.

Practical Implications

Carrying the C allele at rs476828 means your hypothalamic MC4R system operates with reduced receptor density. Satiety signals that would normally be sufficient to stop eating are muted — your brain requires more food intake before the "full" signal reaches threshold. This creates a persistent biological headwind for weight management, but one that responds well to strategies that compensate for weakened internal signals with external structure.

The fat and energy intake data from the women's cohort are particularly actionable: the genetic effect operates partly through appetite drive for energy-dense foods. Interventions that reduce the palatability and caloric density of available food (meal preparation at home, portion pre-commitment, structured eating environments) directly address the mechanism.

The sex-specific neuroimaging data suggest that women with CC genotype may benefit especially from interventions targeting emotional and reward-driven eating, since this is where the documented brain structural differences concentrate.

Interactions

rs17782313 and rs12970134: rs476828 sits in the same regulatory block as these two MC4R-region variants. In Europeans, rs476828 and rs17782313 are in perfect LD (r²=1) — they are interchangeable markers for the same haplotype. The three-SNP haplotype C–C–A (rs17782313–rs476828–rs12970134) carries the highest obesity risk (OR=1.796), while individual SNP effects are smaller. Carrying risk alleles at all three does not simply stack independent risks; they largely reflect the same underlying regulatory signal.

FTO rs9939609: The combined effect¹³¹³ combined effect
documented across multiple populations of MC4R and FTO risk alleles exceeds either alone — MC4R acts through appetite suppression while FTO acts through thermogenesis, so the two pathways are partially independent and their effects add. Combined risk genotypes in one pediatric study conferred 2.45-fold increased obesity odds. Addressing both pathways simultaneously — appetite structure for MC4R, thermogenic activity for FTO — provides complementary benefit.