Conditions Methylmalonic Acidemia (Cobalamin Disorders)

Methylmalonic acidemia (MMA) is a condition with many different forms, which all have different causes and treatments. Methylmalonic acidemia caused by cobalamin disorders A and B is just one type of MMA. To learn about other types of MMA, read about methylmalonic acidemia caused by methylmalonyl-CoA mutase deficiencies or about methylmalonic acidemia with homocystinuria, which is caused by cobalamin disorders C, D, and F.

MMA is an inherited condition in which the body is unable to break down certain fats and proteins. It is considered an organic acid condition because it can lead to a harmful amount of organic acids and toxins in the body. MMA caused by cobalamin A or cobalamin B deficiencies is one type of methylmalonic acidemia. Children with this form of the condition have trouble producing cobalamin enzymes A and B. Cobalamin enzymes are necessary for the body to break down certain foods.

Condition Type

Organic Acid Conditions


Methylmalonic acidemia (MMA) is estimated to affect one out of every 50,000 to 100,000 babies born in the United States. MMA is caused by cobalamin disorders A and B is only one form of methylmalonic acidemia. It is currently unknown the exact number of individuals affected by this specific form.

Also known as

  • Cbl A,B
  • Methylmalonic aciduria
  • CblA or cblB type
  • Adenosylcobalamin deficiency
  • Cobalamin A,B
  • Methylmalonic acidemia

Follow-Up Testing

Your baby’s doctor may ask you if your baby is showing any of the signs of MMA (see Early Signs). If your baby has certain signs, your baby’s physician may suggest starting immediate treatment.

If your baby’s newborn screening result for methylmalonic acidemia (MMA) was out of the normal range, your baby’s doctor or the state screening program will contact you to arrange for your child to have additional testing. It is important to remember that an out-of-range screening result does not necessarily mean that your child has the condition. An out-of-range result may occur because the initial blood sample was too small or the test was performed too early. However, a few babies do have the condition, so it is very important that you go to your follow-up appointment for a confirmatory test. Because the harmful effects of untreated MMA can occur within days after birth, follow-up testing must be completed as soon as possible to determine whether or not your baby has the condition.

Follow-up testing will involve checking your baby’s urine and blood samples for harmful amounts of acids and toxins. Certain acids and toxins build up in the body when a child has an organic acid condition, so studying the levels of these substances in your baby’s body can help doctors determine if your child has a condition. High levels of acylcarnitine in the blood and organic acids in the urine might indicate that your baby has methylmalonic acidemia. Sometimes follow-up testing may also include testing a very small sample of skin.

About Methylmalonic Acidemia (Cobalamin Disorders)

Early Signs

The signs of methylmalonic acidemia cobalamin A and B disorders (Cbl A, B) can begin at any time from birth to adulthood. In most cases, signs first appear during infancy (as early as the first few days after birth).

For babies, signs of Cbl A, B can include

  • Sleeping longer or more often
  • Vomiting
  • Weak muscle tone (also called hypotonia)
  • Fever
  • Breathing trouble
  • Increased number of illnesses and infections
  • Increased bleeding and bruising

Many of these signs may occur when your baby eats foods that their body cannot break down. They can be triggered by long periods of time without eating, illnesses, and infections.

If your baby shows any of these signs, be sure to contact your baby’s doctor immediately.


Supplements and Medications

There are two types of methylmalonic acidemia (MMA): cobalamin disorders and MUT deficiencies. One of the ways these two types of MMA differ is their response to vitamin B-12. MUT deficiencies are considered non-vitamin B-12 responsive.

Cobalamin deficiencies are vitamin B-12 responsive. In these cases, vitamin B-12 injections can prevent symptoms. This type of treatment is more successful for cobalamin A disorders than for colbalamin B disorders, but it is helpful for both.

Your baby’s doctor might also recommend L-carnitine supplements. These supplements help the body break down fats and they can remove harmful substances from the body. Your baby’s doctor will need to write a prescription for these supplements.

Antibiotics can also help to reduce methylmalonic acid levels.

Dietary Treatment

Your baby will need a very carefully monitored diet. Children with MMA need to avoid certain fats and proteins because their bodies cannot break down these substances. Your baby’s doctor can recommend special formulas made for babies with organic acid conditions. These formulas will likely need to be continued through adulthood.

It is also important for your baby to eat frequently. Long periods without food, illnesses, and infection may trigger many of the signs mentioned in the Early Signs section.

Expected Outcomes

Children who receive early and ongoing treatment can have typical development and lead healthy lives. The earlier you start treatment, the better the outcome will be for your baby.

Even with treatment, it is possible for children with methylmalonic acidemia cobalamin disorders A and B (Cbl A,B) to still have some learning disabilities or developmental delays.

It is important to screen for and treat Cbl A and B because, if not treated, children can develop breathing troubles or permanent brain damage.


When we eat food, enzymes help to break it down. Some enzymes break down proteins into their building blocks, amino acids. Other enzymes break down these amino acids. In methylmalonic acidemia cobalamin disorders A and B (Cbl A, B), the enzymes “cobalamin A” and “cobalamin B” are not working correctly.

Cobalamin A and Cobalamin B enzymes help break down amino acids.

Children with Cbl A, B either do not make enough or make non-working Cobalamin A or Cobalamin B enzymes. When these enzymes do not work, their bodies cannot break down the amino acids isoleucine, valine, methionine, and threonine. This causes a build-up of harmful substances in the body.

Cbl A, B is an autosomal recessive genetic condition. This means that a child must inherit two copies of the non-working gene for Cbl A, B, one from each parent, in order to have the condition. The parents of a child with an autosomal recessive condition each carry one copy of the non-working gene, but they typically do not show signs and symptoms of the condition. While having a child with Cbl A, B is rare, when both parents are carriers, they can have more than one child with the condition. Learn more about autosomal recessive inheritance.

Support for Methylmalonic Acidemia (Cobalamin Disorders)

Support Services

Support groups can help connect families who have a child or other family member affected with methylmalonic acidemia with a supportive community of people who have experience and expertise in living with the condition. These organizations offer resources for families, affected individuals, health care providers, and advocates.

Accessing Care

Work with your baby’s doctor to determine the next steps for your baby’s care. Your baby’s doctor may help you coordinate care with a physician who specializes in metabolism, a dietician who can help plan your child’s specialized diet, or other medical resources in your community. Some children with methylmalonic acidemia (MMA) have developmental delays. If you think that your baby is not meeting their developmental milestones, ask your baby’s doctor about the next steps in accessing a developmental evaluation and care.

Because MMA is a genetic condition, you may want to talk with a genetics specialist. A genetic counselor or geneticist can help you understand the causes of the condition, discuss genetic testing for methylmalonic acidemia, and understand what this diagnosis means for other family members and future pregnancies. Speak with your baby’s doctor about getting a referral. The Clinic Services Search Engine offered by the American College of Medical Genetics and Genomics (ACMG) and the Find a Genetic Counselor tool on the National Society of Genetic Counselors (NSGC) website are two good resources for you or your baby's health care provider to use to identify local specialists.

Families' Experiences

You can read stories on the Organic Acidemia Association website by clicking on the family photos at the bottom of this page of the OAA website.

A website called also publishes stories of families affected by methylmalonic acidemia.

References & Sources

Visit MedlinePlus Genetics for more condition information

Visit the Screening, Technology And Research in Genetics (STAR-G) Project for more information on Cbl A,B

Visit GeneReviews for more information on methylmalonic acidemia

ACT Sheets

Healthcare professionals can learn more about confirmatory testing by reading the American College of Medical Genetics and Genomics' Algorithm for Diagnosis and ACT Sheet, a guide for follow-up after newborn screening. You can visit this page of the ACMG website here.

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