General Condition Information
- Methylmalonic acidemia
- Methylmalonic acidemia (methylmalonyl-CoA mutase deficiency)
- Methylmalonic acidemia (methymalonyl-CoA mutase deficiency)
- Methylmalonic acidemia (MUT)
- Methylmalonic acidemia (mutase deficiency form)
- Methylmalonic acidemia (mutase deficiency)
- Methylmalonic acidemia due to mutase deficiency
- Methylmalonic acidemia methylmalonyl-CoA mutase
- Methylmalonic acidemia mutase deficiency
- Methylmalonic acidemia – mutase deficiency
- Methylmalonic acidemia, methylmalonyl-CoA mutase
- Methylmalonic acidemia, mutase deficiency form
- Methylmalonic acidemia- methylmalonyl- CoA mutase
- Methylmalonic acidemia- mutase deficiency
- Methylmalonic acidemia/methylmalonyl-CoA mutase
- Methylmalonic acidemia: methylmalonyl-CoA mutase deficiency
- Methylmalonic acidemia: mutase deficiency
- Methylmalonyl-CoA mutase deficiency
- About 80 to 150 babies are born with methylmalonic acidemia each year in the United States. It is not known exactly how many babies are born with the methylmalonyl-CoA mutase type of methylmalonic acidemia.
- Visit GeneReviews to learn more about how often this condition occurs.
What is Methylmalonic acidemia (methylmalonyl-CoA mutase)
There are different forms of methylmalonic acidemia, each with different causes and treatments. Methylmalonic acidemias are inherited (genetic) conditions that prevent the body from breaking down certain proteins, cholesterol, and fats.
Methylmalonic acidemias happen when an enzyme called methylmalonyl CoA mutase (mut) does not work correctly. This enzyme uses vitamin B-12 to help digest certain proteins, fats, and cholesterol to use them or get rid of them.
Methylmalonic acidemia (methylmalonyl-CoA mutase) is a type of methylmalonic acidemia where this enzyme is not made by the body correctly. To learn about another type of methylmalonic acidemia, visit the Methylmalonic Acidemia (Cobalamin) Disorders page.
Without enough working methylmalonyl CoA mutase, your baby will have trouble making energy and getting rid of waste. This condition can be more or less severe depending on how well this enzyme works. If the baby cannot make any enzyme, the condition is called mut0, which is the most severe form. The condition is called mut- when the baby can make some enzyme that works.
If your baby’s body cannot break down proteins, lipids, and cholesterol, toxins can build up. When these toxins are acids, blood can become acidic (acidemia). Acidemia can damage your baby’s body and lead to the signs and symptoms of the condition.
Newborn Screening and Follow-Up
Newborn screening for methylmalonic acidemia is done using a small amount of blood collected from your baby’s heel. To learn more about this process, visit the Blood Spot Screening page.
During screening, a special machine measures how much of certain substances (called acylcarnitines) are in your baby’s blood. Your body produces these substances when it breaks down fats. Specific organic acids (called methylmalonic acid and methylcitric acid) may also be measured. Babies with high levels of these substances might have methylmalonic acidemia.
If your baby’s blood spot screening result for methylmalonic acidemia is out-of-range, your baby’s health care provider will contact you. Together, you will discuss next steps and follow-up plans.
An out-of-range screening result does not mean that your baby definitely has the condition. It does mean that your baby needs more follow-up testing. To learn more about screening results, visit the Blood Spot Screening Results page.
Your baby may need any of the following tests after an out-of-range screening result:
- Blood and urine tests
- Genetic testing using a blood sample
- Small skin sample
You should complete any recommended follow-up testing as soon as possible. Babies with this condition can have very serious health problems early in life if they are not diagnosed and treated quickly.
False-positive newborn screening results for this condition can happen. Some situations can affect screening results, including:
Newborn screening helps babies lead healthier lives. If your baby has an out-of-range result, follow up with your health care provider quickly. It is important to follow their instructions. Your baby may need to get treatment right away, even if they are not showing signs or symptoms. In some cases, your baby’s health care provider may decide it is best to watch (monitor) your baby to decide next steps. Careful monitoring and early treatment will help your baby stay as healthy as possible.
Signs of methylmalonic acidemia can vary widely and usually start within the first few days to months of life. Symptoms can be caused by eating foods that the body cannot break down or by long periods without eating. Symptoms can also be brought on by illness or infection. Milder forms of methylmalonic acidemia may not appear until later in infancy or childhood.
Signs of the condition may include the following:
Methylmalonic acidemia (methylmalonyl-CoA mutase) is caused by changes in the MMUT gene. The MMUT gene gives your body instructions for making the enzyme methylmalonyl CoA mutase.
Without a working MMUT gene, your baby's body cannot make enough working methylmalonyl CoA mutase. As a result, their body has trouble breaking down proteins, lipids, and cholesterol. Their body cannot make enough energy, and harmful toxins build up and damage their body.
- Methylmalonic acidemia is an autosomal recessive condition. Babies inherit the condition when each parent passes down a nonworking MMUT gene to their baby. Only babies with two nonworking MMUT genes—one from the mom and one from the dad—have this condition.
- People with one working copy and one nonworking copy of the MMUT gene are called carriers.
- Carriers do not have or develop the condition. However, they may pass down a nonworking copy of the gene to their children.
- If two parents are carriers of a nonworking copy of the MMUT gene, they have a 1 in 4 chance of having a child with methylmalonic acidemia.
- Carriers for methylmalonic acidemia often do not know they are carriers before having a child with the condition. In most cases, families have no history of the condition until the birth of a child with methylmalonic acidemia.
- Parents who already have a child with methylmalonic acidemia still have a 1 in 4 chance of having another child with methylmalonic acidemia. This 1 in 4 chance stays the same for all future children.
- Genetic counselors and medical geneticists can help families learn about this condition and the chance of having children with it. Visit the National Society of Genetic Counselors to find a genetic counselor and the American College of Medical Genetics and Genomics to find a medical geneticist.
Treatment and Management
It is important to talk to your health care provider about which treatment(s) are best for your baby. The goal of treatment is to prevent the health problems caused by this condition.
Treatments may include the following:
- Diet low in certain proteins and fats
- Special formulas and foods
- Regular and frequent meals and snacks
- Vitamin B-12 supplements (only for certain types of methylmalonic acidemia), usually given by a shot (injection) rather than by mouth
- Carnitine supplements in some cases
Children who receive early and ongoing treatment for methylmalonic acidemia can have healthy growth and development. Even with treatment, some children may still have developmental delays or learning difficulties.