Date Updated: 05/30/2020


Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency is an inherited disorder that prevents your body from breaking down certain fats and converting them into energy. As a result, the level of sugar in your blood can drop dangerously low (hypoglycemia). MCAD deficiency is present from birth and is a lifelong condition.

Left untreated, hypoglycemia caused by MCAD deficiency can lead to seizures, breathing difficulties, coma and other serious health problems.

In the U.S., all states test for MCAD deficiency at birth as part of newborn screening. If MCAD deficiency is diagnosed and treated early, the disorder can be well managed through diet and lifestyle.


Signs and symptoms of MCAD deficiency typically first appear in babies and young children. In rare cases, the disorder is not diagnosed until adulthood.

Signs and symptoms can vary among people with MCAD deficiency, but they typically include:

  • Vomiting
  • Lack of energy
  • Low blood sugar (hypoglycemia)

Hypoglycemia can be triggered by:

  • Going too long without eating or by fasting
  • Not eating enough complex carbohydrates
  • Viral infections and other illnesses
  • Recurrent fever
  • Vomiting
  • Diarrhea
  • Increased exercise
  • Vaccinations
  • Significant stress

Sometimes episodes of hypoglycemia can occur with no symptoms in between these episodes.

When to see a doctor

In the U.S., all newborn screening programs now test for MCAD deficiency. If you notice signs and symptoms of MCAD deficiency or if you have concerns about your child's health, contact your doctor. After the initial evaluation, you may be referred to a doctor trained in evaluating and treating MCAD deficiency and other health care team members such as a dietitian.


When you don't have enough of the MCAD enzyme in your body, certain fats called medium-chain fatty acids can't be broken down and converted to energy. This results in hypoglycemia and low energy. Also, fatty acids can build up in body tissues and cause damage to the liver and brain.

MCAD deficiency is inherited from both parents. Though both parents are carriers — each one has an abnormal gene — they typically don't have symptoms of the condition. The affected child inherits two copies of the abnormal gene — one from each parent.

If you inherit only one affected gene, you won't develop MCAD deficiency, but you are a carrier and can pass the abnormal gene to your children. But they wouldn't develop the condition unless they also inherited an affected gene from their other parent.


If the hypoglycemia caused by MCAD deficiency is left untreated, it can lead to:

  • Seizures
  • Breathing problems
  • Liver problems
  • Brain damage
  • Coma
  • Sudden death


MCAD deficiency is diagnosed through newborn screening followed by genetic testing.

  • Newborn screening. In the U.S., all states screen for MCAD deficiency at birth. If screening levels are abnormal, additional testing can be done.
  • Genetic testing. Genetic testing can reveal the abnormal gene that causes MCAD deficiency. Depending on the type of test, a sample of blood, skin or other tissue is collected and sent to a lab for analysis. Your doctor may also recommend testing family members for this gene. Talk with your doctor, a medical geneticist or a genetic counselor about the testing process and what the results mean.

Episodes of low blood sugar (hypoglycemia) thought to be caused by MCAD deficiency are evaluated by a discussion of signs and symptoms, as well as dietary habits, usually followed by lab tests to identify problems with metabolism and treat or prevent complications.


Newborn screening at birth allows MCAD deficiency to be diagnosed and treated early, before symptoms occur, preventing complications. Once identified, the disorder can be managed through diet and lifestyle.

The main goal of treatment for MCAD deficiency is to prevent problems caused by hypoglycemia from occurring. Infants with MCAD deficiency require frequent feedings with adequate calories from complex carbohydrates to maintain blood sugar and avoid hypoglycemia. Children and adults also require adequate complex carbohydrates on a regular schedule of eating. Work with your health care team, including a dietitian, to develop a treatment plan tailored to your childꞌs or your metabolic needs.

The length of time that is safe for fasting may vary with age and your health care teamꞌs recommendations. For example, during the first four months of life, well infants' fasting time may be no longer than four hours. Fasting time may be gradually increased up to 12 hours by one year of age. Children and adults should not fast for longer than 12 hours.

Recommendations to prevent hypoglycemia generally include:

  • Avoid fasting longer than recommended by your health care team
  • Eat regular meals and snacks with adequate calories from complex carbohydrates, such as brown bread, rice, pasta and cereal, for energy needs
  • Choose foods that are high in complex carbohydrates and lower in fat
  • Increase calories by eating extra complex carbohydrates during illness, stress or increased activity

Your health care team may recommend a carnitine supplement to aid in fatty acid metabolism.

Talk with your doctor about what to do if hypoglycemia signs and symptoms develop so that you have an emergency plan. Strategies may include:

  • Taking simple carbohydrates, such as sugar (glucose) tablets or sweetened, nondiet beverages.
  • Seeking emergency medical care if unable to eat or for diarrhea or vomiting. An intravenous (IV) line for extra glucose and additional treatment may be needed.

Lifestyle and home remedies

Parent and family understanding of the condition is critical to ongoing care and prevention of hypoglycemia episodes and complications. Prevention tips include:

  • Avoid fasting
  • Know the warning signs of hypoglycemia and treat it immediately
  • Eat complex carbohydrates before extra activity or exercise
  • Increase calories with extra complex carbohydrates during illness, stress or increased activity
  • Always carry complex carbohydrate snacks
  • Always carry a source of simple carbohydrates to treat hypoglycemia

If you or your child has been diagnosed with MCAD deficiency, wear a medical alert bracelet or necklace or carry a medical card. This lets health care providers know of your condition, even in an emergency. Ask your doctor about information for health care professionals that you can carry with you in case your child needs emergency care.

Coping and support

Caring for a child or family member with a lifelong disorder such as MCAD deficiency can be stressful and exhausting. Consider these strategies:

  • Learn about the disorder. Learn as much as you can about MCAD deficiency. Then you can make the best choices and be an advocate for yourself or your child. Help family members, caregivers, teachers and friends understand the condition, the care needed, and the consequences of not following dietary instructions.
  • Find a team of trusted professionals. You'll need to make important decisions every day about care. Medical centers with specialty teams can offer you information about the disorder, as well as nutritional advice and support, and can help you manage care.
  • Seek out other families. Talking to people who are dealing with similar challenges can provide you with information and emotional support. Ask your doctor about support groups in your community. If a group isn't for you, maybe your doctor can put you in touch with a family who has dealt with the disorder. Or you may be able to find a group or individual support online.
  • Ask for help from family and friends. Ask for or accept help from family and friends in caring for your loved one when needed. Take time for your own interests and activities. Counseling with a mental health professional may help with adjustment and coping.

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