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

May 30, 2020
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