Overview
Methylmalonic acidemia without homocystinuria (also called isolated methylmalonic acidemia or MMA) is a rare inherited metabolic disorder in which the body cannot properly break down certain proteins and fats. This happens because an enzyme called methylmalonyl-CoA mutase does not work correctly, or because the body cannot make enough of a special form of vitamin B12 (called adenosylcobalamin) that this enzyme needs. When this enzyme is not working, a substance called methylmalonic acid builds up in the blood and tissues, which can be toxic to many organs, especially the brain and kidneys. Symptoms often appear in the first days to months of life and can include poor feeding, vomiting, extreme tiredness, low muscle tone, and developmental delays. During times of illness or stress, patients can experience life-threatening metabolic crises with dangerously high acid levels in the blood. Over time, the disease can cause kidney problems, neurological complications, and growth delays. Treatment focuses on preventing metabolic crises through a carefully controlled low-protein diet, special medical formulas, and in some cases vitamin B12 supplementation. Some patients respond well to B12 therapy (these are called B12-responsive forms), while others do not respond and require stricter dietary management. Liver and sometimes kidney transplantation may be considered in severe cases. Newborn screening programs in many countries now detect this condition early, which allows treatment to begin before serious damage occurs.
Also known as:
Key symptoms:
Poor feeding and refusal to eatFrequent vomitingExtreme tiredness and lethargyLow muscle tone (floppy baby)Developmental delaysFailure to grow and gain weight properlySeizuresKidney problemsMetabolic crises with high acid in the bloodDehydrationBreathing difficultiesIntellectual disabilityMovement problemsEnlarged liverLow blood cell counts
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
No FDA-approved treatments are currently listed for Methylmalonic acidemia without homocystinuria.
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Specialists
View all specialists →No specialists are currently listed for Methylmalonic acidemia without homocystinuria.
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 Methylmalonic acidemia without homocystinuria.
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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.Is my child's form of methylmalonic acidemia responsive to vitamin B12 treatment?,What specific gene mutation is causing the condition, and what does that mean for severity?,What should our emergency sick-day plan look like, and when should we go to the hospital?,How often will my child need blood tests and kidney function monitoring?,Should we consider liver or kidney transplantation, and when would that be recommended?,Are there any clinical trials or new treatments available that we should know about?,What developmental and educational support services should we arrange?
Common questions about Methylmalonic acidemia without homocystinuria
What is Methylmalonic acidemia without homocystinuria?
Methylmalonic acidemia without homocystinuria (also called isolated methylmalonic acidemia or MMA) is a rare inherited metabolic disorder in which the body cannot properly break down certain proteins and fats. This happens because an enzyme called methylmalonyl-CoA mutase does not work correctly, or because the body cannot make enough of a special form of vitamin B12 (called adenosylcobalamin) that this enzyme needs. When this enzyme is not working, a substance called methylmalonic acid builds up in the blood and tissues, which can be toxic to many organs, especially the brain and kidneys. Sy
How is Methylmalonic acidemia without homocystinuria inherited?
Methylmalonic acidemia without homocystinuria follows a autosomal recessive inheritance pattern. Genetic counseling can help families understand recurrence risk and testing options.