Overview
Hypermethioninemia due to glycine N-methyltransferase (GNMT) deficiency is an extremely rare inherited metabolic disorder that affects how the body processes the amino acid methionine. Methionine is a building block of protein that we get from food, and the body normally breaks it down through a series of chemical steps. The GNMT enzyme plays an important role in this process. When GNMT is missing or not working properly, methionine and a related substance called S-adenosylmethionine (SAM) build up to abnormally high levels in the blood. Most individuals identified with this condition have been found through newborn screening programs that detect elevated methionine levels. The condition appears to be relatively mild in many cases. Some affected individuals have shown mild liver problems, such as elevated liver enzymes or mild hepatomegaly (enlarged liver), while others have remained largely without symptoms. There have been very few patients reported in the medical literature, so the full range of possible symptoms and long-term outcomes is not yet completely understood. There is currently no specific cure for GNMT deficiency. Management typically involves monitoring methionine levels in the blood and may include dietary modification to limit methionine intake. Regular follow-up with a metabolic specialist is recommended to watch for any liver-related complications. Because so few cases have been described, treatment approaches are largely based on individual patient needs rather than established guidelines.
Key symptoms:
High methionine levels in the bloodMildly elevated liver enzymesEnlarged liver (hepatomegaly)Mild liver inflammationElevated S-adenosylmethionine levels in the bloodOften no obvious symptoms (asymptomatic)
Autosomal recessive
Passed on when both parents carry the same gene change; often skips generations
Variable
Can begin at different ages, from infancy through adulthood
Treatments
1 availablePHYTONADIONE PHYTONADIONE
hypoprothrombinemia due to antibacterial therapy
Clinical Trials
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Specialists
View all specialists →No specialists are currently listed for Hypermethioninemia due to glycine N-methyltransferase deficiency.
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
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Caregiver Resources
NORD Caregiver Resources
Support, advocacy, and financial assistance for caregivers of rare disease patients.
Mental Health Support
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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.How high are my (or my child's) methionine and SAM levels, and what do these numbers mean?,Is a methionine-restricted diet necessary, and if so, how strict does it need to be?,How often should blood tests and liver function monitoring be done?,What signs or symptoms should I watch for that would require urgent medical attention?,Are there any long-term complications I should be aware of?,Should other family members be tested for this condition or carrier status?,Are there any research studies or clinical trials available for this condition?
Common questions about Hypermethioninemia due to glycine N-methyltransferase deficiency
What is Hypermethioninemia due to glycine N-methyltransferase deficiency?
Hypermethioninemia due to glycine N-methyltransferase (GNMT) deficiency is an extremely rare inherited metabolic disorder that affects how the body processes the amino acid methionine. Methionine is a building block of protein that we get from food, and the body normally breaks it down through a series of chemical steps. The GNMT enzyme plays an important role in this process. When GNMT is missing or not working properly, methionine and a related substance called S-adenosylmethionine (SAM) build up to abnormally high levels in the blood. Most individuals identified with this condition have be
How is Hypermethioninemia due to glycine N-methyltransferase deficiency inherited?
Hypermethioninemia due to glycine N-methyltransferase deficiency follows a autosomal recessive inheritance pattern. Genetic counseling can help families understand recurrence risk and testing options.