MCAD: Medium Chain acyl CoA Dehydrogenase – Information for Families

Charles R. Roe, MD [Dr Roe is now retired from the Institute of Metabolic Disease in Dallas, TX]

Medium chain acyl CoA dehydrogenase deficiency, or ‘MCAD,’ is a disorder in which your body is unable to breakdown fats to make energy. Normally, fat is broken down into energy by “enzymes.” This energy keeps your body running whenever it runs out of its main source of energy, a sugar called ‘glucose.’ In MCAD, a very important enzyme for breaking down fat, the medium chain acyl CoA dehydrogenase enzyme (MCAD) is missing or does not work correctly. This means that people with MCAD can’t break down fat for energy when they run out of glucose.

Children with MCAD usually get sick for the first time between two months and two years of age but some children get sick as early as two days old or as late as six years old (**be aware that asymptomatic and symptomatic adults are now also being diagnosed, some after having their own MCAD children diagnosed or after an episode). They usually have an illness that makes them not want to eat, like the flu, an ear infection, or a cold. We get worried if children with MCAD have: vomiting. diarrhea, are very, very sleepy or hard to wake up, seizures, or have difficulty breathing. Sometimes a child with MCAD will stop breathing, have seizures, or their heart will stop. Doctors usually check for MCAD deficiency because a child has had these kinds of problems and they can’t find another cause.

MCAD deficiency may be the cause of one out of 100 infant deaths thought to be Sudden Infant Death Syndrome (SIDS). About one fifth of children with MCAD die with their first illness, before anyone knows that they have MCAD deficiency. These children are often completely well until right before they become ill and die. After they die, autopsy often shows brain swelling, a big fatty liver, and too much fat in their heart and kidneys. Some children who die are diagnosed incorrectly as having Reye’s syndrome and sudden infant death (SIDS).

MCAD passes from parent to child through ‘genes.’ Genes are the instructions that our bodies use to make us and to keep us running right. Several genes string together like a necklace and makes a bigger instruction ‘booklet’ called a ‘chromosome.’ Normally we have two copies of our genetic material. We have 22 pairs of chromosomes numbered from largest to smallest, 1 to 22. The23rd pair is special because they are different in men and women. The 23rd pair, the X- and the Y- chromosomes, is called the ‘sex chromosome’ because they decide whether a child will be a boy or a girl.

The gene that causes MCAD is chromosome number one. For a child to have MCAD, both chromosome number 1’s must have an abnormal MCAD gene. This is why MCAD is called an ‘autosomal recessive’ disease. Autosomal means it is a condition that affects both boys and girls. Recessive means that both copies of the gene must be abnormal to get the disease. Most parents of affected children only have one abnormal gene for MCAD, and the other gene is normal, so they do not get sick. We call people with only one abnormal gene ‘carriers,’ because they ‘carry’ one copy of a gene that does not work properly on their # 1 chromosome, but do not get sick themselves since their other gene is normal. If both parents are carriers for MCAD, they have a one in four chance of having another child with MCAD. There is also a one in four chance that brothers and sisters of the child with MCAD might also have MCAD, even if they are older and have not been sick.

We test for MCAD by looking for abnormal substances in the blood or urine. Our tests are very good, and almost always right. Some of these tests let us test children for MCAD at birth, before they get sick, on a very small amount of blood, like a finger stick. We can even find out who carries the MCAD mutation, but are not affected with the disease, by looking directly at each family member’s DNA. If a child in the family has died, a piece of tissue or a blood specimen from their autopsy can be used to see if they had MCAD deficiency, When we find out that one person in a family has MCAD deficiency, it is very important that other members of the family be tested for the disease too. Knowing if other children in the family have MCAD is important because with treatment the severe problems from MCAD deficiency can be prevented.

The main treatment is to avoid going without food for more than ten or twelve hours (ie., an overnight fast when well). Children should eat high carbohydrate meals like sugar-containing drinks, cereals, and pastas when they are ill. A low fat diet may be helpful, and a high fat diet should be avoided. Infants less than one year old should continue to have at least one night-time feeding, or a late night snack, as they should not go even twelve hours without eating. Please read ‘MCAD Information for Clinicians’ (on this site) to understand important emergency room procedures for the MCAD child.

Some doctors who take care of children with MCAD use a drug called L-Carnitine, which helps them keep from getting low blood sugar when they have infections or when they don’t eat. In general, experience in taking care of patients with MCAD suggests that L-Carnitine is very useful in preventing problems with low blood sugar. L-Carnitine is a substance made by the body that carries wastes out of your body’s cells and into your urine. People with MCAD make more toxic wastes than normal people so they need more L-Carnitine than their body can make. When people with MCAD deficiency get sick, are pregnant, or they need to have an operation, they may need even more L-Carnitine than usual. You should never give your child Carnitine that you can buy at the health food store unless you talk to your doctor first. This type of Carnitine may not be L- Carnitine@ and could cause a problem. Please talk with your child’s doctor if you have questions about MCAD or any questions about his or her medications.

A support group for parents and families of children with the medium chain acyl CoA dehydrogenase deficiency and other inherited disorders affecting fat breakdown has been formed by parents of these children. The purpose of the FOD (Fatty Oxidation Disorders) Family Support Group is to allow parents and children (and some adults) with the disorder to talk with each other to provide emotional support and practical information about living with MCAD deficiency (and the other FODs), and to keep families informed regarding new developments in treatment of the disorder.

For more information about this support group, contact Deb Lee Gould at 517.381.1940 or