General Condition Information
- 3 methyl crotonyl CoA carboxylase deficiency
- 3 methylcrotonyl-CoA carboxylase deficiency
- 3-methylcrotonyl CoA carboxylase deficiency
- 3-methylcrotonyl-CoA carboxylase
- 3MCC deficiency
- It is estimated that less than 125 babies are born with this condition each year in the United States.
What is 3-methylcrotonyl-CoA carboxylase deficiency
“3-MCC” is the name of an enzyme in your body that helps you digest a part of some proteins called leucine. This enzyme breaks leucine into smaller pieces that your body can either use or get rid of.
Without enough working 3-MCC enzyme, your baby has trouble using proteins with leucine to make energy. This condition can be more or less severe depending on how well your baby’s 3-MCC enzyme works. Most cases of 3-MCC deficiency are quite mild, with few signs and symptoms.
Newborn Screening and Follow-Up
Newborn screening for 3-MCC deficiency 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. The body produces these substances when it breaks down food. Babies with high levels of these substances might have 3-MCC deficiency.
If your baby’s blood spot screening result for 3-MCC deficiency 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 has the condition. It does mean that your baby needs more follow-up testing. An out-of-range result can mean that your baby has one of several possible conditions. It is important to do follow-up testing to correctly identify the condition causing your baby’s result. To learn more about screening results, visit the Blood Spot Screening Results page.
Your baby may need the following tests after an out-of-range screening result:
- Blood and/or urine tests
- Genetic testing using a blood sample
You should complete any recommended follow-up testing as soon as possible. Babies with this condition may develop health problems if they are not diagnosed and treated quickly.
False-positive newborn screening results for this condition may happen. Babies who are born early (premature) may have out-of-range results.
Some babies may have a false-positive result for 3-MCC deficiency because their mother unknowingly has the condition. These babies do not have and will not develop the condition. More testing on both mom and baby will determine who has high acylcarnitine levels.
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 3-MCC deficiency often appear within the first few months of life but may also appear later in childhood. Some babies with this condition never show any signs.
Signs of the condition may include the following:
- Poor appetite
- Sleeping longer or more often
- Behavior changes
- Gets upset easily
- Floppy arms and legs (hypotonia)
- Muscle tightness (spasticity)
- Delayed growth
- Delayed development
The condition is caused by a change in the MCCC1 or MCCC2 gene. These genes give your body instructions for making the enzyme “3-MCC.” You need this enzyme to digest a part of some proteins called leucine.
When your baby’s MCCC1 or MCCC2 gene is changed, there is not enough normal enzyme to break down leucine. As a result, harmful toxins can build up in their body.
- 3-MCC deficiency is an autosomal recessive condition. Babies inherit the condition when each parent passes down the same nonworking gene that causes methylmalonic acidemia (MCCC1 or MCCC2) to their baby. Only babies with two matching nonworking genes—for example, one nonworking MCCC1 from the mom and one nonworking MCCC1 from the dad—have this condition. Babies with two nonworking genes that do not match—for example, one nonworking MCCC1 from the mom and one nonworking MCCC2 from the dad—will not have this condition.
- People with one working copy and one nonworking copy of the MCCC1 or MCCC2 gene are called carriers.
- Carriers do not have the condition and will not 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 MCCC1 or MCCC2 gene, they have a 1 in 4 chance of having a child with 3-MCC deficiency.
- Carriers for 3-MCC deficiency 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 3-MCC deficiency.
- Parents who already have a child with 3-MCC deficiency still have a 1 in 4 chance of having another child with 3-MCC deficiency 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.
Treatment options can include the following:
- Frequent feedings to avoid long periods without food
- L-carnitine supplements
Children who receive early and ongoing treatment for 3-MCC deficiency can have healthy growth and development.