THE MC4R PATHWAY

Understanding rare melanocortin-4
receptor (MC4R) pathway diseases

The MC4R pathway plays a pivotal role in the underlying biology of many forms of hyperphagia (pathological, insatiable hunger) and obesity. We are committed to using our growing understanding of this pathway to develop new therapeutic options to relieve the substantial burden of living with these rare diseases.

Alastair Garfield, Ph.D.

Chief Scientific Officer

The MC4R pathway: A step-by-step guide

MC4R pathway

The MC4R pathway in the hypothalamus is a key signalling pathway responsible for regulating hunger, food [caloric] intake, and energy expenditure, which consequently affects body weight.1

Leptin

The pathway involves the hormone leptin which is produced by adipose (fat) tissue. In the hypothalamus, a key part of the brain that helps regulate hunger, leptin activates the MC4R pathway causing a cascade of chemical changes that reduce appetite and increase energy expenditure.1,2

Energy balance

Disruption of the MC4R pathway may lead to dysregulation of energy balance, characterized by increased energy intake due to hyperphagia (pathological, insatiable hunger) and/or decreased energy expenditure, ultimately resulting in significant weight gain.

The MC4R pathway explained

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Rare MC4R pathway diseases: A simplified overview

Rare MC4R pathway diseases are caused by genetic variants or physical injury or structural abnormality of the hypothalamus and differ from general obesity. Rare MC4R pathway diseases generally arise because of the following:3-5

Rare, highly impactful variants in genes involved in the MC4R pathway can lead to diseases such as LEPR deficiency or Bardet-Biedl syndrome

An acquired injury to, or structural abnormality within the hypothalamic region may impair MC4R pathway activation which can lead to hyperphagia (pathological, insatiable hunger), decreased energy expenditure and accelerated and sustained weight gain

Cardinal symptoms of rare MC4R pathway diseases

Variants in genes in the MC4R pathway can lead to hyperphagia
(pathological, insatiable hunger) and early-onset obesity.6

Hyperphagia1,2

A chronic disease in which a lack of effective satiety signals and permanent pathological insatiable hunger lead to abnormal food intake and persistent, obsessive food-seeking behaviours.

Early-onset obesity1

The presence of obesity before age 5

Hyperphagia

Hyperphagia is a chronic disease in which a lack of effective satiety signals and permanent pathological insatiable hunger
lead to abnormal food intake and persistent, obsessive food-seeking behaviours.2

Hyperphagia can be characterized by the following:9 

Increased food intake

Nocturnal eating and stealing and hiding of food

Impaired satiety

Excessive food seeking behaviour

Intense preoccupation with food

Extreme distress if food is denied

Craving Answers?

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Path4HCPs

If you are a healthcare professional based outside of the US and would like to discover more about the MC4R pathway, rare MC4R pathway diseases and their management, visit our healthcare professional website:

Path4HCPs

References

 
  • 1.

    Fonseca ACP, et al. J Diabetes Complications. 2017;31(10):1549–1561

  • 2.

    Yazdi F, et al. Peer J. 2015;3:e856

  • 3.

    Huvenne H, et al. Obes Facts. 2016; 9(3):158–173

  • 4.

    Haqq AM, et al., Lanc Diab & Endo. 2022 ; 10(12) :859-868

  • 5.

    Kim JH, Choi JH. Annals of Pediatric End. 2013;(18):161-167

  • 6.

    Hampl SE, et al. Pediatrics. 2023;151(2):e2022060640;2.

  • 7.

    Littleton H., et al., Mol Diagn Ther. 2020;24(6):653-663

  • 8.

    Müller HL et al. Diagnostic criteria for acquired hypothalamic obesity – international expert guidance document. Endocr J. 2025

  • 9.

    Zorn S, et al. Appetite. 2022;178:106-161