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Mayo Clinic Health Library

MCAD deficiency

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.



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.