MCAD Deficiency
Medium-chain acyl-coenzyme A dehydrogenase (MCAD) deficiency is an inherited disorder that prevents your body from breaking down certain fats and turning them into energy. Your metabolism involves the processes your body uses to produce energy. MCAD deficiency can cause problems with your metabolism.
If left untreated, MCAD deficiency may lead to severe lack of energy and tiredness, liver disease, coma, and other serious health problems. Also, the level of sugar in your blood can drop dangerously low — a condition called hypoglycemia. Prevention and prompt treatment are essential regardless of blood sugar level. If you have MCAD deficiency, a sudden episode, called a metabolic crisis, can be caused by common illnesses, high fever, stomach problems or going too long without eating, known as prolonged fasting.
MCAD deficiency is present from birth and is a lifelong condition. In the United States, all states test for MCAD deficiency at birth as part of newborn screening. Many other countries also provide routine newborn screening for MCAD deficiency. If MCAD deficiency is diagnosed and treated early, the disorder can be well managed through diet and lifestyle.
MCAD deficiency is usually first identified in babies and young children. In rare cases, the disorder is not diagnosed until adulthood.
Symptoms can vary among people with MCAD deficiency. They may include:
- Vomiting.
- Low or no energy.
- Weak feeling.
- Low blood sugar.
A sudden severe episode, called a metabolic crisis, can be due to:
- Going too long without eating.
- Missing meals.
- Common infections.
- High fever.
- Ongoing stomach and digestive problems that may cause vomiting and diarrhea.
- Intense exercise.
When to see a doctor
In the United States and many other countries, newborn screening programs test for MCAD deficiency. After your first evaluation, you may be referred to a specialist in evaluating and treating MCAD deficiency. You may also be referred to other health care team members, such as a registered dietitian.
Contact your health care team if you’ve been diagnosed with MCAD deficiency and have a high fever, no appetite, stomach or digestive symptoms, or a planned medical procedure that requires fasting.
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 turned into energy. This leads to low energy and low blood sugar. Also, fatty acids can build up in body tissues and cause damage.
MCAD deficiency is caused by a change in the ACADM gene. The condition is inherited from both parents in an autosomal recessive pattern. This means that both parents are carriers — each has one changed gene and one unchanged gene — but they don’t have symptoms of the condition. The child with MCAD deficiency inherits two copies of the changed gene — one from each parent.
If you inherit only one changed gene, you won’t develop MCAD deficiency. With one changed gene, you are a carrier and can pass the changed gene to your children. But they wouldn’t develop the condition unless they also inherited a changed gene from their other parent.
A child is at risk of MCAD deficiency if both parents are carriers of a gene known to cause it. The child then inherits two copies of the gene — one from each parent. Children who inherit only one copy of the affected gene from one parent typically won’t develop MCAD deficiency but will be carriers of the gene.
If metabolic crisis caused by MCAD deficiency is left untreated, it can lead to:
- Seizures.
- Liver problems.
- Brain damage.
- Coma.
- Sudden death.
MCAD deficiency is diagnosed through newborn screening followed by genetic testing.
- Newborn screening. Many countries, including all states in the United States, screen for MCAD deficiency at birth. Using a heel prick, a few drops of your baby’s blood are taken and analyzed. If screening levels are outside the standard range, additional testing can be done.
- Genetic testing. Genetic testing can reveal the changed gene that causes MCAD deficiency. Depending on the type of test, a sample of blood or saliva or cells from the inside of the cheek, the skin or other tissue is collected and sent to a lab to be tested. Your health care provider may also recommend testing family members for this gene. Genetic counseling can help you understand the testing process and what the results mean.
A metabolic specialist, and often a registered dietitian, are usually included in your diagnosis and treatment. Lab tests can be done to help identify problems with your metabolism — the processes your body uses to produce energy. Results can help 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 your metabolism that can lead to low blood sugar. To maintain blood sugar levels and avoid hypoglycemia:
- Infants require frequent feedings that include getting enough calories from complex carbohydrates.
- Children and adults need to get enough complex carbohydrates on a regular schedule of meals and snacks.
Your health care team may recommend additional treatment options.
Work with your health care team, including a registered dietitian, to develop a treatment plan tailored to your energy needs. This includes planning for extra complex carbohydrates needed during illness, stress or increased activity.
Limit fasting
The length of time that is safe for fasting — going without eating — may vary with age and your health care teamꞌs recommendations. For example, during the first 4 months of life, well infants’ fasting time may be no longer than two to three hours. Fasting time may be gradually increased up to 12 hours by 1 year of age. Children and adults should not fast for longer than 12 hours.
Prevent hypoglycemia
Recommendations to prevent low blood sugar called 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 and before going to sleep.
- Limit alcohol use.
Treat hypoglycemia
Talk with your health care provider about what to do if symptoms of low blood sugar develop so that you have an emergency plan. Strategies may include:
- Taking simple carbohydrates, such as sugar (glucose) tablets or sweetened beverages, such as juice, that are not labeled “diet.”
- Seeking emergency medical care if you can’t eat or if you have diarrhea or vomiting. An intravenous (IV) line for extra glucose and additional treatment may be needed.
References
- Adam MP, et al., eds. Medium-chain acyl-coenzyme A dehydrogenase deficiency. In: GeneReviews. University of Washington, Seattle; 1993-2022. https://www.ncbi.nlm.nih.gov/books/NBK1116/. Accessed Feb. 2, 2022.
- Medium-chain acyl-coenzyme A dehydrogenase deficiency. Genetic and Rare Diseases Information Center. https://rarediseases.info.nih.gov/diseases/540/medium-chain-acyl-coenzyme-a-dehydrogenase-deficiency. Accessed Jan. 20, 2023.
- Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency full gene analysis. Mayo Clinic Laboratories. https://www.mayocliniclabs.com/test-catalog/Clinical+and+Interpretive/35478. Accessed Feb. 2, 2022.
- Anderson DR, et al. Clinical and biochemical outcomes of patients with medium-chain acyl-CoA dehydrogenase deficiency. Molecular Genetics and Metabolism. 2020; doi:10.1016/j.ymgme.2019.11.006.
- McGregor TL, et al. Management principles for acute illness in patients with medium-chain acyl-coenzyme A dehydrogenase deficiency. Pediatrics. 2021; doi:10.1542/peds.2020-040303.
- Piercy H, et al. “It’s just always eating”: The experiences of young people growing up medium chain acyl-CoA dehydrogenase deficiency. Global Qualitative Nursing Research. 2021; doi:10.1177/23333936211032203.
- Advisory Committees on Heritable Disorders in Newborns and Children. Recommended uniform screening panel. Health Resources & Services Administration. https://www.hrsa.gov/advisory-committees/heritable-disorders/rusp/index.html. Accessed Jan. 21, 2023.
- Rucklova K, et al. Impact of newborn screening on early dietary management on clinical outcome of patients with long chain 3-hydroxyacyl-CoA dehydrogenase deficiency and medium chain acyl-CoA dehydrogenase deficiency ⸺ A retrospective nationwide study. Nutrients. 2021; doi:10.3390/nu13092925.
- Medical review (expert opinion). Mayo Clinic. April 11, 2022.
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