Medical Conditions

Methylmalonic Acidemia (MMA) in Babies

Medically reviewed by Dr. Michael Okonkwo, MD, FAAP · Board-Certified Neonatologist

Content reviewed against published NIH, HRSA, ACMG guidelines

Editorial policy

Last reviewed:

If your baby has been diagnosed with or you suspect methylmalonic acidemia (mma) in babies, here is what the evidence says.

The short answer

Methylmalonic acidemia (MMA) is an inherited organic acid disorder in which the body cannot properly process certain amino acids and fats, leading to a buildup of methylmalonic acid. Like propionic acidemia, it typically presents in the first days of life with poor feeding, vomiting, lethargy, and metabolic acidosis. Some forms of MMA respond to vitamin B12 (cobalamin) supplementation, which can significantly improve outcomes. All forms require lifelong dietary management. Kidney disease is a common long-term complication. MMA is detected on newborn screening, and gene therapy research is actively underway.

Key takeaways

  • Methylmalonic acidemia (MMA) is an inherited organic acid disorder in which the body cannot properly process certain amino acids and fats, leading to a buildup of methylmalonic acid. Like propionic acidemia, it typically presents in the first days of life with poor feeding, vomiting, lethargy, and metabolic acidosis. Some forms of MMA respond to vitamin B12 (cobalamin) supplementation, which can significantly improve outcomes. All forms require lifelong dietary management. Kidney disease is a common long-term complication. MMA is detected on newborn screening, and gene therapy research is actively underway.
  • Usually normal when: Your baby's newborn screening came back normal for MMA
  • Call your doctor if: Your newborn is lethargic, feeding poorly, vomiting, and has rapid breathing — a metabolic crisis needs emergency evaluation immediately
  • Varies by age — see the age-by-age breakdown below
“Fever itself is not an illness — rather, it is a sign or symptom that the body is fighting an infection. Fever stimulates certain defenses, such as the white blood cells, which attack and destroy invading bacteria.”
— Fever and Your Child, American Academy of Pediatrics (AAP)

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What Parents Should Know

According to NIH, HRSA, ACMG guidelines, methylmalonic acidemia (MMA) is an inherited organic acid disorder in which the body cannot properly process certain amino acids and fats, leading to a buildup of methylmalonic acid. Like propionic acidemia, it typically presents in the first days of life with poor feeding, vomiting, lethargy, and metabolic acidosis. Some forms of MMA respond to vitamin B12 (cobalamin) supplementation, which can significantly improve outcomes. All forms require lifelong dietary management. Kidney disease is a common long-term complication. MMA is detected on newborn screening, and gene therapy research is actively underway. At 0-1 week, babies with severe MMA often present in the first 24-72 hours of life with feeding difficulty, vomiting, lethargy, and dehydration. Metabolic acidosis develops rapidly, and without treatment, the baby can progress to coma. Lab findings include elevated methylmalonic acid in blood and urine, metabolic acidosis, and often elevated blood ammonia. Emergency treatment involves stopping protein intake, providing IV glucose and fluids, and correcting acidosis. A trial of intramuscular vitamin B12 (hydroxocobalamin) is given to determine if the baby has a B12-responsive form. It is generally considered normal when your baby's newborn screening came back normal for MMA. However, you should contact your pediatrician promptly if your newborn is lethargic, feeding poorly, vomiting, and has rapid breathing — a metabolic crisis needs emergency evaluation immediately.

Sources: [1], [2], [3]

Normal vs. Concerning

Usually Normal
Worth Discussing
Your baby's newborn screening came back normal for MMA
Your newborn is lethargic, feeding poorly, vomiting, and has rapid breathing — a metabolic crisis needs emergency evaluation immediately
An initial positive screen was followed by confirmatory testing that was normal — mildly elevated methylmalonic acid can sometimes be a false positive or a benign variant
Your baby with known MMA is ill and unable to eat or keep food down for more than a few hours — go to the emergency room with your metabolic emergency letter for IV glucose
Your baby has a B12-responsive form of MMA and is stable on B12 supplementation with normal growth and development
Your child with MMA becomes increasingly lethargic, develops seizures, or shows a significant change in alertness or behavior — call 911 and inform them your child has a metabolic disorder
Your child with MMA is on dietary treatment and metabolic markers and kidney function are in the target range
Your child with MMA develops severe abdominal pain, persistent vomiting unrelated to illness, or signs of kidney failure (decreased urination, swelling, fatigue)

When to Seek Immediate Care

  • Your newborn is lethargic, feeding poorly, vomiting, and has rapid breathing — a metabolic crisis needs emergency evaluation immediately
  • Your baby with known MMA is ill and unable to eat or keep food down for more than a few hours — go to the emergency room with your metabolic emergency letter for IV glucose
  • Your child with MMA becomes increasingly lethargic, develops seizures, or shows a significant change in alertness or behavior — call 911 and inform them your child has a metabolic disorder
  • Your child with MMA develops severe abdominal pain, persistent vomiting unrelated to illness, or signs of kidney failure (decreased urination, swelling, fatigue)

By Age

What to expect by age

0-1 week

Babies with severe MMA often present in the first 24-72 hours of life with feeding difficulty, vomiting, lethargy, and dehydration. Metabolic acidosis develops rapidly, and without treatment, the baby can progress to coma. Lab findings include elevated methylmalonic acid in blood and urine, metabolic acidosis, and often elevated blood ammonia. Emergency treatment involves stopping protein intake, providing IV glucose and fluids, and correcting acidosis. A trial of intramuscular vitamin B12 (hydroxocobalamin) is given to determine if the baby has a B12-responsive form.

1-6 months

After stabilization, the metabolic team determines the specific type of MMA through genetic testing and B12 responsiveness testing. B12-responsive forms generally have a milder course and are managed with regular B12 injections plus moderate protein restriction. Non-responsive forms (mut0 and mut-) require strict dietary protein restriction using specialized metabolic formulas. Carnitine supplementation is standard. Feeding and growth are closely monitored. Metabolic crises remain a risk during any illness.

6-12 months

As with propionic acidemia, introducing solid foods requires careful coordination with the metabolic dietitian. Protein intake must be measured precisely. Most nutrition comes from specialized metabolic formula. Developmental monitoring is important — some babies with MMA develop normally, while others may have developmental delays or learning difficulties, particularly those with the severe non-responsive forms. Renal function should be monitored regularly, as kidney complications can begin early.

1-5 years

Dietary management continues lifelong. Metabolic crises during illness remain the greatest acute risk. Kidney function must be monitored regularly because progressive renal insufficiency is common in mut0 MMA and can eventually require dialysis or kidney transplant. Some children undergo combined liver-kidney transplant to address both the metabolic defect and kidney disease. Movement disorders, particularly affecting gait and coordination, may develop due to basal ganglia injury. Pancreatitis is an uncommon but recognized complication.

Long-term considerations

Long-term outcomes for MMA have improved significantly with early detection through newborn screening and better metabolic management. Kidney disease remains the most significant long-term complication for severe forms. Liver transplant can reduce metabolic crises but does not fully correct the underlying defect, and kidney disease may still progress. Gene therapy and mRNA therapy approaches are in active clinical trials and represent promising future treatments. Regular monitoring by metabolic specialists, nephrologists, and neurologists is essential.

What to Tell Your Pediatrician

  • Describe when you first noticed methylmalonic acidemia (mma) in babies and how it has changed over time.
  • Note your baby's current age and which age-specific patterns you are seeing.
  • Mention if your baby received an abnormal MMA result on newborn screening — follow up promptly for confirmatory testing and specialist evaluation.
  • Mention if your baby with MMA has metabolic markers consistently outside the target range or declining kidney function.
  • Let your doctor know if you have noticed any related concerns, such as changes in feeding, sleep, or movement patterns.
  • Bring a list of any questions or observations you want to discuss at the appointment.

What Should You Do?

When to take action

Probably normal when...
  • Your baby's newborn screening came back normal for MMA
  • An initial positive screen was followed by confirmatory testing that was normal — mildly elevated methylmalonic acid can sometimes be a false positive or a benign variant
  • Your baby has a B12-responsive form of MMA and is stable on B12 supplementation with normal growth and development
  • Your child with MMA is on dietary treatment and metabolic markers and kidney function are in the target range
Mention at your next visit when...
  • Your baby received an abnormal MMA result on newborn screening — follow up promptly for confirmatory testing and specialist evaluation
  • Your baby with MMA has metabolic markers consistently outside the target range or declining kidney function
  • Your child with MMA has new difficulty with coordination, walking, or motor skills that may indicate basal ganglia involvement
  • You have questions about liver or kidney transplant options for your child with severe MMA
Act now when...
  • Your newborn is lethargic, feeding poorly, vomiting, and has rapid breathing — a metabolic crisis needs emergency evaluation immediately
  • Your baby with known MMA is ill and unable to eat or keep food down for more than a few hours — go to the emergency room with your metabolic emergency letter for IV glucose
  • Your child with MMA becomes increasingly lethargic, develops seizures, or shows a significant change in alertness or behavior — call 911 and inform them your child has a metabolic disorder
  • Your child with MMA develops severe abdominal pain, persistent vomiting unrelated to illness, or signs of kidney failure (decreased urination, swelling, fatigue)

What You Can Do at Home

  • Keep track of when you notice methylmalonic acidemia (mma) in babies — noting the time of day, duration, and any triggers can help your pediatrician.
  • Remember that your baby's newborn screening came back normal for MMA — this is generally within the range of normal.
  • At 0-1 week, focus on observation rather than intervention unless your pediatrician advises otherwise.
  • Follow any care instructions from your pediatrician. Keep a written log of symptoms to bring to appointments.
  • While monitoring at home, seek immediate care if your newborn is lethargic, feeding poorly, vomiting, and has rapid breathing — a metabolic crisis needs emergency evaluation immediately.

Abnormal Newborn Screening Results

An abnormal or positive newborn screening result means that further testing is needed, not that your baby definitely has a condition. Most positive screens turn out to be false positives after confirmatory testing. Newborn screening tests are intentionally sensitive to avoid missing any affected babies, so follow-up testing is essential to determine whether the result is a true positive.

Signs of a Metabolic Disorder in Babies

Metabolic disorders (inborn errors of metabolism) occur when the body cannot properly process certain nutrients or chemicals. Many are detected through newborn screening. Signs can include poor feeding, vomiting, lethargy, seizures, unusual body or urine odor, failure to thrive, developmental regression, and metabolic crises triggered by illness or fasting. Early detection and treatment are crucial, as many metabolic disorders are manageable with dietary modifications and medical treatment.

Milestone

Month-by-Month Development

Detailed monthly development guides from birth through 24 months.

Guide

When to Call the Doctor

General guide on when to call the pediatrician, visit urgent care, or go to the ER.

Frequently asked questions

Is methylmalonic acidemia (mma) in babies normal?
Methylmalonic acidemia (MMA) is an inherited organic acid disorder in which the body cannot properly process certain amino acids and fats, leading to a buildup of methylmalonic acid. Like propionic acidemia, it typically presents in the first days of life with poor feeding, vomiting, lethargy, and metabolic acidosis. Some forms of MMA respond to vitamin B12 (cobalamin) supplementation, which can significantly improve outcomes. All forms require lifelong dietary management. Kidney disease is a common long-term complication. MMA is detected on newborn screening, and gene therapy research is actively underway.
When should I call the doctor about methylmalonic acidemia (mma) in babies?
Your newborn is lethargic, feeding poorly, vomiting, and has rapid breathing — a metabolic crisis needs emergency evaluation immediately Your baby with known MMA is ill and unable to eat or keep food down for more than a few hours — go to the emergency room with your metabolic emergency letter for IV glucose Your child with MMA becomes increasingly lethargic, develops seizures, or shows a significant change in alertness or behavior — call 911 and inform them your child has a metabolic disorder
When is methylmalonic acidemia (mma) in babies normal?
Your baby's newborn screening came back normal for MMA An initial positive screen was followed by confirmatory testing that was normal — mildly elevated methylmalonic acid can sometimes be a false positive or a benign variant Your baby has a B12-responsive form of MMA and is stable on B12 supplementation with normal growth and development
What causes methylmalonic acidemia (mma) in babies?
Methylmalonic acidemia (MMA) is an inherited organic acid disorder in which the body cannot properly process certain amino acids and fats, leading to a buildup of methylmalonic acid. Like propionic acidemia, it typically presents in the first days of life with poor feeding, vomiting, lethargy, and metabolic acidosis. Some forms of MMA respond to vitamin B12 (cobalamin) supplementation, which can significantly improve outcomes. All forms require lifelong dietary management. Kidney disease is a common long-term complication. MMA is detected on newborn screening, and gene therapy research is actively underway. Common explanations include: Your baby's newborn screening came back normal for MMA. An initial positive screen was followed by confirmatory testing that was normal — mildly elevated methylmalonic acid can sometimes be a false positive or a benign variant.
What should I mention to my pediatrician about methylmalonic acidemia (mma) in babies?
You should mention methylmalonic acidemia (mma) in babies at your next visit if: Your baby received an abnormal MMA result on newborn screening — follow up promptly for confirmatory testing and specialist evaluation. Your baby with MMA has metabolic markers consistently outside the target range or declining kidney function. Your child with MMA has new difficulty with coordination, walking, or motor skills that may indicate basal ganglia involvement.
Is methylmalonic acidemia (mma) in babies normal at 0-1 week?
Babies with severe MMA often present in the first 24-72 hours of life with feeding difficulty, vomiting, lethargy, and dehydration. Metabolic acidosis develops rapidly, and without treatment, the baby can progress to coma. Lab findings include elevated methylmalonic acid in blood and urine, metabolic acidosis, and often elevated blood ammonia. Emergency treatment involves stopping protein intake, providing IV glucose and fluids, and correcting acidosis. A trial of intramuscular vitamin B12 (hydroxocobalamin) is given to determine if the baby has a B12-responsive form.
Is methylmalonic acidemia (mma) in babies normal at 1-6 months?
After stabilization, the metabolic team determines the specific type of MMA through genetic testing and B12 responsiveness testing. B12-responsive forms generally have a milder course and are managed with regular B12 injections plus moderate protein restriction. Non-responsive forms (mut0 and mut-) require strict dietary protein restriction using specialized metabolic formulas. Carnitine supplementation is standard. Feeding and growth are closely monitored. Metabolic crises remain a risk during any illness.
Should I go to the ER for methylmalonic acidemia (mma) in babies?
Seek emergency care if your newborn is lethargic, feeding poorly, vomiting, and has rapid breathing — a metabolic crisis needs emergency evaluation immediately, or if your baby with known MMA is ill and unable to eat or keep food down for more than a few hours — go to the emergency room with your metabolic emergency letter for IV glucose. When in doubt, call your pediatrician's after-hours line for guidance.
Does methylmalonic acidemia (mma) in babies go away on its own?
In many cases, methylmalonic acidemia (mma) in babies resolves on its own, especially when your baby's newborn screening came back normal for MMA. By Long-term considerations, long-term outcomes for MMA have improved significantly with early detection through newborn screening and better metabolic management. Kidney disease remains the most significant long-term complication for severe forms. Liver transplant can reduce metabolic crises but does not fully correct the underlying defect, and kidney disease may still progress. Gene therapy and mRNA therapy approaches are in active clinical trials and represent promising future treatments. Regular monitoring by metabolic specialists, nephrologists, and neurologists is essential.
NIHHRSAACMG

References

  1. [1]National Library of Medicine. Methylmalonic Acidemia. MedlinePlus Genetics, 2023. NIH
  2. [2]Health Resources and Services Administration. Methylmalonic Acidemia Fact Sheet. Baby's First Test, 2023. HRSA
  3. [3]American College of Medical Genetics. ACT Sheet: Elevated C3 Acylcarnitine. ACMG, 2023. ACMG

Doctor Visit Checklist

Bring this checklist to your next pediatrician visit to discuss Methylmalonic Acidemia (MMA) in Babies.

Things to mention

  • Describe when you first noticed methylmalonic acidemia (mma) in babies and how it has changed over time.
  • Note your baby's current age and which age-specific patterns you are seeing.
  • Mention if your baby received an abnormal MMA result on newborn screening — follow up promptly for confirmatory testing and specialist evaluation.
  • Mention if your baby with MMA has metabolic markers consistently outside the target range or declining kidney function.
  • Let your doctor know if you have noticed any related concerns, such as changes in feeding, sleep, or movement patterns.
  • Bring a list of any questions or observations you want to discuss at the appointment.

Observations to share

  • Your baby received an abnormal MMA result on newborn screening — follow up promptly for confirmatory testing and specialist evaluation
  • Your baby with MMA has metabolic markers consistently outside the target range or declining kidney function
  • Your child with MMA has new difficulty with coordination, walking, or motor skills that may indicate basal ganglia involvement

Urgent signs to report immediately

  • Your newborn is lethargic, feeding poorly, vomiting, and has rapid breathing — a metabolic crisis needs emergency evaluation immediately
  • Your baby with known MMA is ill and unable to eat or keep food down for more than a few hours — go to the emergency room with your metabolic emergency letter for IV glucose
  • Your child with MMA becomes increasingly lethargic, develops seizures, or shows a significant change in alertness or behavior — call 911 and inform them your child has a metabolic disorder

My notes

From ismybabyalright.com — free, evidence-based baby health guides

All content follows our editorial policy and is reviewed against published clinical guidelines.

2,705 evidence-based guides6 authoritative medical sources5 medical advisory board members

Related Resources

Well-Baby Visit PrepEmergency ContactsBaby Tracker

Bottom line

Most cases of methylmalonic acidemia (mma) in babies are normal. Talk to your pediatrician if your newborn is lethargic, feeding poorly, vomiting, and has rapid breathing — a metabolic crisis needs emergency evaluation immediately.

Trust your instincts. If something feels wrong, reach out to your pediatrician. Worrying about your baby means you care — that is a good thing.

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An abnormal or positive newborn screening result means that further testing is needed, not that your baby definitely has a condition. Most positive screens turn out to be false positives after confirmatory testing. Newborn screening tests are intentionally sensitive to avoid missing any affected babies, so follow-up testing is essential to determine whether the result is a true positive.

Signs of a Metabolic Disorder in Babies

Metabolic disorders (inborn errors of metabolism) occur when the body cannot properly process certain nutrients or chemicals. Many are detected through newborn screening. Signs can include poor feeding, vomiting, lethargy, seizures, unusual body or urine odor, failure to thrive, developmental regression, and metabolic crises triggered by illness or fasting. Early detection and treatment are crucial, as many metabolic disorders are manageable with dietary modifications and medical treatment.

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