RARE DISEASE
Obesity due to melanocortin 4 receptor deficiency
Obesity due to melanocortin 4 receptor deficiency
Obesity due to melanocortin 4 receptor deficiency
Synonyms: MC4R deficiency
Synonyms: MC4R deficiency
Synonyms: MC4R deficiency
Drug discovery
0
drugs
With orphan designations
Overview
Overview of Obesity Due to Melanocortin 4 Receptor Deficiency
MC4R deficiency is the most common monogenic cause of obesity, characterized by severe early-onset hyperphagia, accelerated linear growth in childhood, increased lean mass, and hyperinsulinemia [1][4][10]. It arises from heterozygous or homozygous mutations in the MC4R gene, disrupting hypothalamic appetite regulation. Adults exhibit lower hypertension prevalence but retain metabolic risks like type 2 diabetes and insulin resistance [4][7][9]. Penetrance varies by age, with higher obesity rates in childhood (79%) than older adults (40%) [2][14].
Burden
Comorbidities: Elevated risk of type 2 diabetes (independent of BMI in childhood), hyperleptinemia, and insulin resistance [7][9][16].
Growth and metabolic effects: Increased final adult height, accelerated BMI gain in childhood, and lower blood pressure compared to BMI-matched controls [4][10].
Psychosocial/economic impact: Significant healthcare costs due to early complications (e.g., obstructive sleep apnea, lymphedema) and reduced quality of life [15][16].
Therapies
Lifestyle modifications: Often insufficient due to impaired satiety signaling [4][16].
Pharmacotherapy: GLP-1 agonists (semaglutide, tirzepatide) show efficacy [4]; MC4R agonists (e.g., setmelanotide) are under investigation [8].
Surgery: Roux-en-Y bypass may benefit heterozygous patients but is ineffective in homozygotes [4][16].
Emerging therapies: Preclinical success with BDNF gene therapy targeting MC4R downstream pathways [3][13].
Categories: rare endocrine diseases, rare genetic diseases
Research Papers
605 drug discovery papers about Obesity due to melanocortin 4 receptor deficiency, with 4 first-in-class emerging drug candidates forecasted to outperform the average preclinical success rate. Recent publications:
605 drug discovery papers about Obesity due to melanocortin 4 receptor deficiency, with 4 first-in-class emerging drug candidates forecasted to outperform the average preclinical success rate. Recent publications:
2026-08-07 | Pharmacogenetic hypersensitivity to somatropin in a child with severe growth hormone deficiency and MC4R p.V166I variant.
The melanocortin-4 receptor (MC4R) is a G protein-coupled receptor that regulates energy homeostasis. Pathogenic MC4R variants represent the most common cause of monogenic obesity and are frequently associated with increased linear growth. However, the mechanisms linking MC4R signaling to somatic growth remain incompletely understood. We report a child with severe growth hormone deficiency (GHD) carrying a heterozygous MC4R variant (c.496G>A; p.V166I), in whom recombinant human growth hormone (rhGH) therapy triggered an unexpectedly exaggerated clinical and biochemical response, suggesting a potential pharmacogenetic interaction between MC4R signaling and the GH/IGF-1 axis. The male patient was first evaluated at 1 month of age due to micropenis and diagnosed with multiple pituitary hormone deficiencies. At 57 months of age, his height was 97.3 cm (-2.56 SDS) and annual growth velocity was 4.1 cm/year (<-2 SDS); rhGH (somatropin) therapy was initiated. Despite severe biochemically confirmed GHD, rhGH at 0.03 mg/kg/day triggered an exaggerated response: IGF-1 levels increased from -3.35 SDS to +8.00 SDS. Concurrently, his height velocity accelerated to 16 cm/year, and his bone age rapidly advanced by approximately 4 years over a 23-month period, culminating in mandibular prognathism. The coexistence of severe GHD and an MC4R variant is rarely described, and such a pronounced response to rhGH has not previously been reported. These findings suggest that MC4R p.V166I may modulate peripheral GH/IGF-1 signaling and act as a pharmacogenetic modifier of GH responsiveness. Careful rhGH dose titration with close IGF-1 monitoring may be considered in patients carrying the MC4R p.V166I variant.
2026-07-10 | The application of GLP-1 receptor agonists in obesity due to MC4R deficiency
Although the pathogenesis of genetic obesity is becoming increasingly clear, effective treatments remain lacking, particularly for obesity caused by melanocortin 4 receptor (MC4R) deficiency. The activity of MC4R is strictly regulated by its endogenous ligands: α-melanocyte-stimulating hormone (α-MSH) binds to MC4R and transmits anorexigenic and energy-expenditure signals, whereas agouti-related protein (AgRP) exerts an antagonistic effect by binding to the receptor, competitively inhibiting α-MSH action and promoting appetite. Current options, such as lifestyle modifications and bariatric surgery, have limited efficacy, highlighting the need for accessible pharmacological interventions. This review evaluates glucagon-like peptide-1 (GLP-1) receptor agonists in MC4R-deficient obesity. We conducted a comprehensive literature search across databases, including PubMed and Web of Science, compiling data from clinical trials, case reports, and basic research studies published up to 2025, with a focus on the efficacy, safety, and mechanism of action of drugs such as liraglutide, semaglutide, and tirzepatide in patients with MC4R deficiency. Evidence indicates these agents induce significant weight loss, appetite suppression, and metabolic improvements via mechanisms independent of intact MC4R signaling. Their weight-loss effects are comparable to those seen in common obesity, with additional benefits for comorbidities like insulin resistance and dyslipidemia. These findings support the GLP-1 pathway as an alternative to impaired MC4R, offering a viable treatment. Understanding their efficacy and mechanisms provides new treatment options for this rare condition and offers evidence for genetically specific personalized weight management.
2026-06-24 | Cardiometabolic regulation by adipocyte-derived leptin and the brain melanocortin system.
Tonic activation of central nervous system (CNS) leptin receptors (LepRs) and melanocortin 4 receptors (MC4Rs) is critical for maintaining normal cardiometabolic function. Deficiency of CNS LepR or MC4R signaling causes severe obesity and is accompanied by multiple metabolic abnormalities including insulin resistance, glucose intolerance, and hyperlipidemia that are only partially explained by obesity. Defective LepR and MC4R signaling also causes dysfunction of the sympathetic nervous system (SNS) and blood pressure (BP) regulation. Hyperleptinemia and activation of the CNS melanocortin system in obesity are important compensatory mechanisms that attenuate abnormalities of glucose and lipid metabolism but may also contribute to SNS activation and increased BP. Despite potentially adverse effects of increases in SNS activity and BP, pharmacological activation of brain LepRs and MC4Rs may provide an important therapeutic approach for protecting target organs, such as the heart, kidneys, and brain, from ischemic injury by improving mitochondrial function and ATP production. However, additional preclinical studies are needed to address mechanistic questions before clinical studies are begun to test the effectiveness of leptin and MC4R agonists for treating people with ischemic injury of target organs.
2026-05-27 | SKNY-1, a THCV Analog, Produces Weight Loss, Lipid Normalization and Attenuation of Reward-Associated Behaviors in an mc4r(G894C) Zebrafish Model of Obesity.
Obesity resulting from melanocortin-4 receptor (MC4R) dysfunction is characterized by combined metabolic dysregulation and maladaptive reward-related behaviors that limit the durability of existing therapies. The endocannabinoid system is a central regulator of appetite, lipid metabolism, and reward processing; however, first-generation cannabinoid receptor 1 (CB1) antagonists were limited by adverse neuropsychiatric effects. SKNY-1 is an orally active tetrahydrocannabivarin (THCV) analog designed to engage pathway-biased CB1 signaling, modulate cannabinoid receptor 2 (CB2), and selectively inhibit monoamine oxidase B (MAO-B), with the objective of addressing both metabolic and behavioral components of obesity while minimizing central nervous system liability through biased CB1 signaling, CB2 modulation, and potential complementary MAO-B inhibition. Here, we integrated in vitro pharmacological profiling of SKNY-1 with in vivo evaluation in an adult mc4r(G894C) zebrafish model exhibiting obesity-associated metabolic and reward-related phenotypes. In vitro, SKNY-1 displayed low-potency modulation of CB1 cyclic AMP signaling (EC50 ~30 µM) but more potent antagonism of the CB1 β-arrestin pathway (IC50 ~6 µM), consistent with differential CB1 pathway modulation. SKNY-1 acted as a CB2 partial agonist (EC50 ~0.1 µM), with antagonist activity emerging at higher concentrations, and selectively inhibited MAO-B at low affinity with no activity against MAO-A. In vivo, mc4r(G894C) zebrafish mutants exhibited dyslipidemia, hepatic triglyceride accumulation, altered appetite-regulatory gene expression, increased metabolic rate, and enhanced compulsive high-calorie feeding and nicotine-seeking behaviors. Oral administration of SKNY-1 for six days produced dose-dependent effects. Both doses normalized total cholesterol and low-density lipoprotein levels and reduced hepatic triglycerides toward wild-type values without affecting circulating triglycerides. The higher dose (200 ng per fish per day) induced significant body weight reduction while preserving body density and attenuated reward-associated feeding and nicotine-seeking behaviors. The lower dose (20 ng per fish per day) more effectively normalized the leptin a-to-ghrelin expression ratio. Collectively, these findings demonstrate that SKNY-1 engages integrated endocannabinoid and potential dopaminergic mechanisms to improve metabolic parameters and attenuate maladaptive reward-related behaviors in an MC4R-deficient vertebrate model, supporting its further translational investigation for obesity complicated by compulsive eating and substance-seeking behaviors.
2026-04-21 | Mice lacking β-arrestin-2 in melanocortin 4 receptor-expressing neurons show marked metabolic deficits.
Hypothalamic melanocortin 4 receptors (MC4Rs) play a central role in regulating food intake and energy homeostasis. In fact, inactivating mutations in the MC4R gene are the most common form of monogenic obesity. Agonist activation of MC4Rs reduces food intake by modulating hypothalamic signaling circuits. Thus, a detailed understanding of the signaling pathways that regulate MC4R activity is of considerable translational relevance. Ligand-activated MC4Rs not only interact with heterotrimeric G proteins but also can recruit β-arrestin-2 (barr2) to the receptor. The potential functional role of barr2 in regulating the anorectic effects of MC4R signaling remains unexplored. In the present study, we used mutant mouse models to demonstrate MC4R-mediated activation of barr2/ERK signaling in MC4R neurons of the paraventricular nucleus leads to reduced food intake. We also found the appetite-suppressing effect of setmelanotide, an MC4R agonist FDA approved for the treatment of certain types of obesity, requires the presence of barr2 in MC4R-containing neurons. These data suggest that MC4R agonists able to promote MC4R/barr2 interactions with high efficacy may become useful as appetite-suppressing drugs.
2026-08-07 | Pharmacogenetic hypersensitivity to somatropin in a child with severe growth hormone deficiency and MC4R p.V166I variant.
The melanocortin-4 receptor (MC4R) is a G protein-coupled receptor that regulates energy homeostasis. Pathogenic MC4R variants represent the most common cause of monogenic obesity and are frequently associated with increased linear growth. However, the mechanisms linking MC4R signaling to somatic growth remain incompletely understood. We report a child with severe growth hormone deficiency (GHD) carrying a heterozygous MC4R variant (c.496G>A; p.V166I), in whom recombinant human growth hormone (rhGH) therapy triggered an unexpectedly exaggerated clinical and biochemical response, suggesting a potential pharmacogenetic interaction between MC4R signaling and the GH/IGF-1 axis. The male patient was first evaluated at 1 month of age due to micropenis and diagnosed with multiple pituitary hormone deficiencies. At 57 months of age, his height was 97.3 cm (-2.56 SDS) and annual growth velocity was 4.1 cm/year (<-2 SDS); rhGH (somatropin) therapy was initiated. Despite severe biochemically confirmed GHD, rhGH at 0.03 mg/kg/day triggered an exaggerated response: IGF-1 levels increased from -3.35 SDS to +8.00 SDS. Concurrently, his height velocity accelerated to 16 cm/year, and his bone age rapidly advanced by approximately 4 years over a 23-month period, culminating in mandibular prognathism. The coexistence of severe GHD and an MC4R variant is rarely described, and such a pronounced response to rhGH has not previously been reported. These findings suggest that MC4R p.V166I may modulate peripheral GH/IGF-1 signaling and act as a pharmacogenetic modifier of GH responsiveness. Careful rhGH dose titration with close IGF-1 monitoring may be considered in patients carrying the MC4R p.V166I variant.
2026-07-10 | The application of GLP-1 receptor agonists in obesity due to MC4R deficiency
Although the pathogenesis of genetic obesity is becoming increasingly clear, effective treatments remain lacking, particularly for obesity caused by melanocortin 4 receptor (MC4R) deficiency. The activity of MC4R is strictly regulated by its endogenous ligands: α-melanocyte-stimulating hormone (α-MSH) binds to MC4R and transmits anorexigenic and energy-expenditure signals, whereas agouti-related protein (AgRP) exerts an antagonistic effect by binding to the receptor, competitively inhibiting α-MSH action and promoting appetite. Current options, such as lifestyle modifications and bariatric surgery, have limited efficacy, highlighting the need for accessible pharmacological interventions. This review evaluates glucagon-like peptide-1 (GLP-1) receptor agonists in MC4R-deficient obesity. We conducted a comprehensive literature search across databases, including PubMed and Web of Science, compiling data from clinical trials, case reports, and basic research studies published up to 2025, with a focus on the efficacy, safety, and mechanism of action of drugs such as liraglutide, semaglutide, and tirzepatide in patients with MC4R deficiency. Evidence indicates these agents induce significant weight loss, appetite suppression, and metabolic improvements via mechanisms independent of intact MC4R signaling. Their weight-loss effects are comparable to those seen in common obesity, with additional benefits for comorbidities like insulin resistance and dyslipidemia. These findings support the GLP-1 pathway as an alternative to impaired MC4R, offering a viable treatment. Understanding their efficacy and mechanisms provides new treatment options for this rare condition and offers evidence for genetically specific personalized weight management.
2026-06-24 | Cardiometabolic regulation by adipocyte-derived leptin and the brain melanocortin system.
Tonic activation of central nervous system (CNS) leptin receptors (LepRs) and melanocortin 4 receptors (MC4Rs) is critical for maintaining normal cardiometabolic function. Deficiency of CNS LepR or MC4R signaling causes severe obesity and is accompanied by multiple metabolic abnormalities including insulin resistance, glucose intolerance, and hyperlipidemia that are only partially explained by obesity. Defective LepR and MC4R signaling also causes dysfunction of the sympathetic nervous system (SNS) and blood pressure (BP) regulation. Hyperleptinemia and activation of the CNS melanocortin system in obesity are important compensatory mechanisms that attenuate abnormalities of glucose and lipid metabolism but may also contribute to SNS activation and increased BP. Despite potentially adverse effects of increases in SNS activity and BP, pharmacological activation of brain LepRs and MC4Rs may provide an important therapeutic approach for protecting target organs, such as the heart, kidneys, and brain, from ischemic injury by improving mitochondrial function and ATP production. However, additional preclinical studies are needed to address mechanistic questions before clinical studies are begun to test the effectiveness of leptin and MC4R agonists for treating people with ischemic injury of target organs.
2026-05-27 | SKNY-1, a THCV Analog, Produces Weight Loss, Lipid Normalization and Attenuation of Reward-Associated Behaviors in an mc4r(G894C) Zebrafish Model of Obesity.
Obesity resulting from melanocortin-4 receptor (MC4R) dysfunction is characterized by combined metabolic dysregulation and maladaptive reward-related behaviors that limit the durability of existing therapies. The endocannabinoid system is a central regulator of appetite, lipid metabolism, and reward processing; however, first-generation cannabinoid receptor 1 (CB1) antagonists were limited by adverse neuropsychiatric effects. SKNY-1 is an orally active tetrahydrocannabivarin (THCV) analog designed to engage pathway-biased CB1 signaling, modulate cannabinoid receptor 2 (CB2), and selectively inhibit monoamine oxidase B (MAO-B), with the objective of addressing both metabolic and behavioral components of obesity while minimizing central nervous system liability through biased CB1 signaling, CB2 modulation, and potential complementary MAO-B inhibition. Here, we integrated in vitro pharmacological profiling of SKNY-1 with in vivo evaluation in an adult mc4r(G894C) zebrafish model exhibiting obesity-associated metabolic and reward-related phenotypes. In vitro, SKNY-1 displayed low-potency modulation of CB1 cyclic AMP signaling (EC50 ~30 µM) but more potent antagonism of the CB1 β-arrestin pathway (IC50 ~6 µM), consistent with differential CB1 pathway modulation. SKNY-1 acted as a CB2 partial agonist (EC50 ~0.1 µM), with antagonist activity emerging at higher concentrations, and selectively inhibited MAO-B at low affinity with no activity against MAO-A. In vivo, mc4r(G894C) zebrafish mutants exhibited dyslipidemia, hepatic triglyceride accumulation, altered appetite-regulatory gene expression, increased metabolic rate, and enhanced compulsive high-calorie feeding and nicotine-seeking behaviors. Oral administration of SKNY-1 for six days produced dose-dependent effects. Both doses normalized total cholesterol and low-density lipoprotein levels and reduced hepatic triglycerides toward wild-type values without affecting circulating triglycerides. The higher dose (200 ng per fish per day) induced significant body weight reduction while preserving body density and attenuated reward-associated feeding and nicotine-seeking behaviors. The lower dose (20 ng per fish per day) more effectively normalized the leptin a-to-ghrelin expression ratio. Collectively, these findings demonstrate that SKNY-1 engages integrated endocannabinoid and potential dopaminergic mechanisms to improve metabolic parameters and attenuate maladaptive reward-related behaviors in an MC4R-deficient vertebrate model, supporting its further translational investigation for obesity complicated by compulsive eating and substance-seeking behaviors.
2026-04-21 | Mice lacking β-arrestin-2 in melanocortin 4 receptor-expressing neurons show marked metabolic deficits.
Hypothalamic melanocortin 4 receptors (MC4Rs) play a central role in regulating food intake and energy homeostasis. In fact, inactivating mutations in the MC4R gene are the most common form of monogenic obesity. Agonist activation of MC4Rs reduces food intake by modulating hypothalamic signaling circuits. Thus, a detailed understanding of the signaling pathways that regulate MC4R activity is of considerable translational relevance. Ligand-activated MC4Rs not only interact with heterotrimeric G proteins but also can recruit β-arrestin-2 (barr2) to the receptor. The potential functional role of barr2 in regulating the anorectic effects of MC4R signaling remains unexplored. In the present study, we used mutant mouse models to demonstrate MC4R-mediated activation of barr2/ERK signaling in MC4R neurons of the paraventricular nucleus leads to reduced food intake. We also found the appetite-suppressing effect of setmelanotide, an MC4R agonist FDA approved for the treatment of certain types of obesity, requires the presence of barr2 in MC4R-containing neurons. These data suggest that MC4R agonists able to promote MC4R/barr2 interactions with high efficacy may become useful as appetite-suppressing drugs.
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