Overview
Obesity due to SIM1 deficiency is a rare genetic condition caused by changes (mutations) in the SIM1 gene. SIM1 stands for Single-Minded Homolog 1, and this gene plays an important role in the development and function of a part of the brain called the hypothalamus. The hypothalamus is the brain's control center for hunger, fullness, and energy balance. When the SIM1 gene does not work properly, the brain has trouble regulating appetite, which leads to severe early-onset obesity. Children with this condition typically develop an intense, hard-to-control hunger (called hyperphagia) starting in early childhood. They gain weight rapidly and can become severely obese at a young age. Some individuals may also have mild developmental delays, behavioral challenges, or features that overlap with Prader-Willi-like syndrome, though the severity varies from person to person. Currently, there is no cure for obesity due to SIM1 deficiency. Treatment focuses on managing weight through structured dietary plans, behavioral strategies to control eating, regular physical activity, and close monitoring by a team of specialists. Research into medications that target the brain's appetite pathways, such as setmelanotide (Imcivree), is ongoing and may offer hope for some patients with this type of genetic obesity. Early diagnosis through genetic testing is important so that families can access appropriate support and management strategies as soon as possible.
Key symptoms:
Severe obesity starting in early childhoodExtreme and constant hunger (hyperphagia)Rapid weight gainDifficulty feeling full after eatingMild intellectual disability or learning difficultiesBehavioral problems such as stubbornness or emotional outburstsFeatures resembling Prader-Willi syndromeIncreased risk of type 2 diabetesHigh blood pressureSleep apneaJoint pain or mobility problems due to excess weightLow muscle tone in infancy
Clinical phenotype terms (17)— hover any for plain English
Autosomal dominant
Passed on from just one parent; each child has about a 50% chance of inheriting it
Childhood
Begins in childhood, roughly ages 1 to 12
Treatments
No FDA-approved treatments are currently listed for Obesity due to SIM1 deficiency.
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Specialists
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Treatment Centers
8 centersBaylor College of Medicine Rare Disease Center ↗
Baylor College of Medicine
📍 Houston, TX
🏥 NORDStanford Medicine Rare Disease Center ↗
Stanford Medicine
📍 Stanford, CA
🔬 UDNNIH Clinical Center Undiagnosed Diseases Program ↗
National Institutes of Health
📍 Bethesda, MD
🔬 UDNUCLA UDN Clinical Site ↗
UCLA Health
📍 Los Angeles, CA
🔬 UDNBaylor College of Medicine UDN Clinical Site ↗
Baylor College of Medicine
📍 Houston, TX
🔬 UDNHarvard/MGH UDN Clinical Site ↗
Massachusetts General Hospital
📍 Boston, MA
🏥 NORDMayo Clinic Center for Individualized Medicine ↗
Mayo Clinic
📍 Rochester, MN
👤 Mayo Clinic Center for Individualized Medicine
🏥 NORDUCLA Rare Disease Day Program ↗
UCLA Health
📍 Los Angeles, CA
Travel Grants
No travel grants are currently matched to Obesity due to SIM1 deficiency.
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Caregiver Resources
NORD Caregiver Resources
Support, advocacy, and financial assistance for caregivers of rare disease patients.
Mental Health Support
Rare disease caregiving can be isolating. Connect with counseling and peer support.
Family & Caregiver Grants
Financial assistance programs specifically for caregivers of rare disease patients.
Social Security Disability
Learn how rare disease patients may qualify for SSDI/SSI benefits.
Questions for your doctor
Bring these to your next appointment
- Q1.Is my child's obesity caused by a change in the SIM1 gene, and how was this confirmed?,Are there any medications, such as setmelanotide, that might help control my child's hunger?,What kind of diet and exercise plan do you recommend for my child?,Should we screen for complications like diabetes, high blood pressure, or sleep apnea, and how often?,Are there clinical trials or new treatments being studied for SIM1-related obesity?,Should other family members be tested for changes in the SIM1 gene?,Can you refer us to a behavioral psychologist experienced with genetic obesity?
Common questions about Obesity due to SIM1 deficiency
What is Obesity due to SIM1 deficiency?
Obesity due to SIM1 deficiency is a rare genetic condition caused by changes (mutations) in the SIM1 gene. SIM1 stands for Single-Minded Homolog 1, and this gene plays an important role in the development and function of a part of the brain called the hypothalamus. The hypothalamus is the brain's control center for hunger, fullness, and energy balance. When the SIM1 gene does not work properly, the brain has trouble regulating appetite, which leads to severe early-onset obesity. Children with this condition typically develop an intense, hard-to-control hunger (called hyperphagia) starting in
How is Obesity due to SIM1 deficiency inherited?
Obesity due to SIM1 deficiency follows a autosomal dominant inheritance pattern. Genetic counseling can help families understand recurrence risk and testing options.
At what age does Obesity due to SIM1 deficiency typically begin?
Typical onset of Obesity due to SIM1 deficiency is childhood. Age of onset can vary across affected individuals.