G
Genetic Archaeology
GENETIC ARCHAEOLOGY // PROFILE

MC4R

Melanocortin 4 Receptor

CHR 18
18q21.32

Overview

The MC4R gene encodes the melanocortin-4 receptor, a central switch for appetite and energy balance in the hypothalamus. It is the most common monogenic cause of severe obesity and a key therapeutic target.

📍 Position
18q21.32 (Chromosome 18)
🏷️ Category
Metabolism
⚡ Receptor Type
G-protein coupled receptor
📊 Frequency
C-allele ~25-35% (BMI effect)

The Leptin-Melanocortin Pathway

MC4R is the endpoint of a crucial satiety signaling pathway:

Adipose Tissue
Leptin ↑

→

POMC Neurons
α-MSH Production

→

MC4R
Receptor Activated

→

Satiety
Appetite ↓, Energy Expenditure ↑
💡 Alpha-MSH (Melanotropin): Cleaved from POMC, it activates MC4R. This signals the brain: “Energy stores are full, eat less and burn more.”

🧬 Genetic Variant

rs17782313
18:60162664
(150kb downstream)
Lower Risk

T

/

Higher Risk

C

~150kb downstream of MC4R: The C-allele is strongly associated with increased BMI and obesity risk by influencing MC4R expression.

C-Allele (25-35%):

  • ~0.5 kg/m² higher BMI
  • ~1-3 kg higher body weight
  • Increased lifetime risk of obesity
  • Preference for dietary fats
⚠️ Monogenic MC4R Defects: Rare loss-of-function mutations in MC4R cause 1-6% of all severe obesity cases (massive appetite since early childhood, hyperphagia, frequent eating).

🍽️ Appetite & Nutrition

C-Allele Carriers (25-35%)

  • Increased feeling of hunger
  • Preference for high-fat foods
  • Reduced satiety after meals
  • Tendency toward “rebound hunger”
  • Easier weight gain

T/T (Lower Risk)

  • Normal satiety mechanism
  • Satiety reached more easily
  • No increased risk through this variant

💊 Pharmacology: Setmelanotide

In 2020, Setmelanotide (Imcivree) was approved as the first MC4R agonist medication:

✅ Indication: Chronic weight management in patients 6 years and older with monogenic forms of obesity (POMC, PCSK1, or LEPR deficiency).
  • Mechanism: Setmelanotide bypasses defective POMC signals and activates MC4R directly
  • Efficacy: ~10% weight loss in genetically matched patients
  • Limitation: Ineffective in MC4R mutations themselves (missing receptor)
  • Side Effects: Skin pigmentation (typical of melanotropin), nausea, depression

✅ Lifestyle Recommendations

For C-Allele Carriers:

  • High-protein diet: Protein activates alternative satiety mechanisms (GLP-1, PYY)
  • Fiber-rich foods: Dietary fiber promotes fullness and delays gastric emptying
  • Regular meals: Avoid hypoglycemia that triggers cravings
  • Higher food volume: Low-calorie-dense foods to fill the stomach
  • Exercise: Increases GLP-1 and PYY, supporting alternative satiety pathways
💡 Important: The effect of rs17782313 is polygenically small (~0.5 kg/m²). Lifestyle interventions can completely override this effect! Genetics is a factor of tendency, not destiny.

📚 Data Sources

  • OMIM: #155541 (MC4R Gene)
  • dbSNP: rs17782313
  • PubMed: Loos et al. (2008) – Common variants near MC4R
  • NEJM: Setmelanotide trials (2020)
  • Nature Genetics: GWAS for BMI and obesity

Last Update: February 2026

Biological Function

MC4R is activated by Alpha-MSH and suppresses appetite in the arcuate nucleus of the hypothalamus. It is part of the leptin-melanocortin pathway. Weight-increasing variants lead to increased appetite, reduced satiety, and hyperphagia. The I251V (rs17782313) and V103I variants are the most common SNPs associated with BMI.

Associated Conditions

Obesity (monogenic, rare) Overweight (polygenic) Hyperphagia (increased hunger) Insulin Resistance
Molecular Analysis

Analyzed Markers

rs17782313 Risk Factor
Pos: 18:60162664 | Alleles: T/C

~150kb downstream of MC4R - C-allele strongly associated with increased BMI (+0.5 kg/m²), higher lifetime risk of obesity, and preference for dietary fat. Effect via influencing MC4R expression.