Medium-chain ketoacyl-CoA thiolase (MCKAT) deficiency is a condition that prevents the body from breaking down certain fats and turning them into energy. If the body does not make enough energy from fat, substances build up in the blood and can cause serious health problems.

It is unknown how many babies are born with this rare condition each year in the United States.

In MCKAT deficiency, the medium-chain ketoacyl-CoA thiolase enzyme is not working correctly. This enzyme helps the body break down certain fats. When the MCKAT enzyme does not work, substances called “medium chain fatty acids” build up in the body. The buildup of medium chain fatty acids leads to the signs and symptoms of the condition.

Many newborn screening conditions are genetic, so babies inherit conditions from their biological (birth) parents. Because MCKAT deficiency is so rare, we do not currently understand or know what gene causes it.

Most of what is known about MCKAT is from one reported case. In this case, signs of the condition began showing when the baby was 2 days old.

Signs of the condition may include the following:

• Breathing problems
• Vomiting
• Low blood sugar (hypoglycemia)
• Diarrhea
• Weight loss
• Poor appetite

Newborn screening for MCKAT 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 makes energy from fats. Babies with high levels of these substances might have MCKAT deficiency.

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

If your baby’s blood spot screening result for MCKAT 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 blood and/or urine tests if they have an out-of-range screening result.

You should complete any recommended follow-up testing as soon as possible. Babies with this condition can have serious health problems soon after birth if they are not diagnosed and treated quickly.

There have been only very few reported cases of this condition, so there is no information on false-positive newborn screening results.

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.

The goal of treatment is to prevent the health problems caused by this condition. MCKAT deficiency is so rare that there are no standard treatments. It is important to talk to your health care provider about treatment(s) that are best for your baby.