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Medium-Chain Acyl-CoA Dehydrogenase Deficiency
Wednesday, 17 November 2004
Wednesday, 17 November 2004


Medium-Chain Acyl-CoA Dehydrogenase (MCAD) deficiency is a rare, inherited condition that results when this enzyme is missing or poorly functioning. MCAD is most active in the liver and is needed to break down fat for energy when sugar is not available. Normally, fat gets broken down into ketones about 8 hours after fasting (or not eating). Individuals affected with MCAD cannot break down fat to make energy when they don’t eat for long periods of time because they are missing this important enzyme. This makes them at risk for developing low blood sugar. Also, since they cannot break down these fats, the fatty molecules accumulate abnormally in the liver and the brain. MCAD deficiency was first described in 1976.


One in 4,900-17,000 newborns has MCAD deficiency. It is more common in Caucasians. Girls and boys are affected equally.

Signs and Symptoms

Approximately 70% of babies with MCAD deficiency will never develop symptoms. In the remaining 30%, symptoms typically begin to develop between 2 months and 2 years of life. Some people may not develop symptoms until adulthood. Symptoms are triggered by low blood sugar levels due to fasting, stress or infection. The baby or child may show irritability, vomiting, jitteriness, sweating, lethargy, seizures, and/or difficulty breathing. The liver may become large or not function well in some children. In severe cases, coma or sudden death can occur.

Possible Causes

MCAD deficiency is inherited in an autosomal recessive manner. This means that each parent carries one abnormal copy of the MCAD gene and one normal copy. Since each parent has one normal copy of the gene, they are usually healthy. But if the child gets two abnormal copies of the gene (one from each parent), the child is affected with MCAD deficiency. When both parents are carriers, there is a 25% chance of each of their children developing this disease. There is a 67% chance that unaffected children will be carriers. MCAD deficiency is not contagious or preventable. One in 40-100 healthy people are carriers of MCAD deficiency. The gene for MCAD is located on chromosome 1.


Blood testing during fasting will show low blood sugar levels and high levels of ammonia. Blood and urine testing will show inappropriately low or absent ketones. Also, blood and urine carnitine levels will be low. The diagnosis can be confirmed by showing low MCAD enzyme activity on skin biopsy which is a procedure that takes a tiny piece of skin from under the arm to analyze. More than 9 states in the U.S. currently test for MCAD deficiency as part of their newborn screening.


The aim of treatment is to avoid low blood sugar levels. It is very important to avoid long periods of fasting, especially during illness or stress. Infants should be fed every 4 hours during the day and every 5-6 hours overnight. After six months of age, overnight feeding can be stretched to every 8 hours. Cornstarch can be given before bedtime to decrease the frequency of low blood sugar levels in the morning. In older children, fasting should not exceed 12 hours. Intake of carbohydrates should be increased during illness and stress. If the child is unable to drink during illness, intravenous sugar is crucial. High intake of dietary fat should be avoided. Oral carnitine supplements reduce the frequency and severity of episodes. If there are any developmental problems, it is important that the child receive help such as physical therapy, occupational therapy, and/or speech therapy. Individuals should have an “emergency” letter that they can give to health care workers which explains MCAD deficiency and how to manage it in the event of an emergency.


When treated appropriately, the majority of children do well. Prolonged episodes of low blood sugar can cause brain damage and result in developmental and behavioral problems, muscle weakness, cerebral palsy, difficulty walking, attention deficit disorder, and poor growth. A quarter of patients may die before diagnosis with their first episode of illness.

Connect with other parents

In the spirit of community and support, Madisons Foundation offers the unique service of connecting parents of children with rare diseases. If you would like to be connected to other parents of children with this disease, please fill out this brief form.


Fatty Oxidation Disorders (FOD) Family Support Group
International coalition providing resources, education, and networking.

Organic Acidemia Association
Voluntary support group which represents children and adults with these disorders, their families and caregivers.

United Mitochondrial Disease Foundation
Non-profit organization providing support groups, education, information about research studies, counseling, and family networking.

CLIMB (Children Living with Inherited Metabolic Diseases)
ational organization providing information, news, financial support, and networking.

March of Dimes Birth Defects Foundation
Non-profit organization providing support groups, education, information about research studies, counseling, and family networking.

NIH/National Institute of Diabetes, Digestive and Kidney Diseases Endocrine Diseases Metabolic Diseases Branch
organization providing information, support, and newsletters.

Google Search for Medium-Chain Acyl-CoA Dehydrogenase Deficiency

References and Sources