Malonyl-CoA decarboxylase deficiency is an inherited (genetic) condition that prevents the body from breaking down certain fats and turning them into energy.

Malonyl-CoA decarboxylase is an enzyme that helps you digest a type of fat called fatty acids. Without functioning malonyl-CoA decarboxylase, the body has trouble breaking down fats. This condition can be more or less severe depending on how well the enzyme works.

Breaking down fat for energy allows the body to work properly, and breaking down fat is especially important after a long time without food (fasting) and during illness. If your body does not make enough energy from fat, blood sugar levels can drop to dangerously low levels.

If the body cannot process fats properly, waste and toxins can build up, and damage your baby’s heart. If untreated, this damage leads to the signs and symptoms of the condition.

Malonyl-CoA decarboxylase deficiency is caused by a change in the MLYCD gene. This gene gives the body instructions to make malonyl-CoA decarboxylase. This enzyme helps your body break down certain fats for energy.

Without a working MLYCD gene, your baby’s body cannot make malonyl-CoA decarboxylase enzyme that works well. As a result, they cannot properly break down fats to make energy and get rid of toxins.

Malonyl-CoA decarboxylase deficiency is a genetic condition. Babies inherit it from their biological (birth) parents.

• Malonyl-CoA decarboxylase deficiency is usually an autosomal recessive condition. Babies inherit the condition when each parent passes down a nonworking MLYCD gene to their baby. Only babies with two nonworking MLYCD genes—one from the mom and one from the dad—have this condition.
  • People with one working copy and one nonworking copy of the MLYCD 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 MLYCD gene, they have a 1 in 4 chance of having a child with malonyl-CoA decarboxylase deficiency.
  • Carriers for malonyl-CoA decarboxylase 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 malonyl-CoA decarboxylase deficiency.
  • Parents who already have a child with malonyl-CoA decarboxylase deficiency due to a change in the MLYCD gene still have a 1 in 4 chance of having another child with malonyl-CoA decarboxylase 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.

Signs of malonyl-CoA decarboxylase deficiency can appear anytime between the first few days of life up to adolescence. Signs typically appear early in childhood.

Signs of the condition may include the following:

• Developmental delays
• Floppy arms and legs (hypotonia)
• Low blood sugar (hypoglycemia)
• Diarrhea
• Vomiting
• Weak and large heart (cardiomyopathy)
• Seizures

Newborn screening for malonyl-CoA decarboxylase deficiency is done using a small amount of blood collected from your baby’s heel. 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 food. Babies with high levels of these substances might have malonyl-CoA decarboxylase deficiency.

What Happens After an Out-of-Range Screening Result?

If your baby’s blood spot screening result for malonyl-CoA decarboxylase 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 definitely has the condition. It does mean that your baby needs more follow-up testing.

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 can have serious health problems if they are not diagnosed and treated.

False-positive newborn screening results for this condition are rare.

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.

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:

• Low-fat diet
• Frequent feedings to avoid long periods without food
• L-carnitine supplements

Children who receive early and ongoing treatment for malonyl-CoA decarboxylase deficiency can have healthy growth and development.