Myths vs facts: MC4R and sleep

MC4R (melanocortin-4 receptor) is a well-established regulator of energy balance and appetite; loss-of-function mutations are the most common monogenic cause of early-onset obesity. Claims that MC4R variants directly and meaningfully affect sleep are not supported by robust evidence. While some GWAS have reported weak associations with sleep duration or quality, effect sizes are tiny (<1% variance) and replication is inconsistent. Mechanistic links (e.g., via leptin-melanocortin pathways) are speculative. No RCTs demonstrate that MC4R genotype predicts response to sleep interventions. Direct-to-consumer tests marketing MC4R as a 'sleep gene' overstate the science. Sleep hygiene, light exposure, and circadian routines dominate sleep outcomes. Genetic testing for MC4R in the context of sleep is not clinically indicated and lacks guideline support. Bottom line: MC4R is an obesity gene, not a sleep gene. The evidence for a sleep role is unclear and not actionable.