Medium-Chain Acyl-Coenzyme A Dehydrogenase (MCAD) Deficiency is one of the most common inherited disorders of fatty acid oxidation. Although babies with MCAD deficiency usually appear completely healthy at birth, the condition can become life-threatening if it is not recognised early. Fortunately, newborn screening and appropriate management have dramatically improved outcomes, allowing most people with MCAD deficiency to live healthy, normal lives.
What is MCAD Deficiency?
MCAD deficiency is a rare genetic condition that affects the body’s ability to break down medium-chain fatty acids for energy. Normally, when a person goes without food for several hours, such as overnight or during illness, the body switches from using glucose to burning stored fat. People with MCAD deficiency cannot efficiently use medium-chain fats as an energy source because they lack sufficient activity of the medium-chain acyl-CoA dehydrogenase enzyme.
As a result, the body can rapidly run out of available energy, particularly during periods of fasting, vomiting, or increased metabolic stress.
What Causes MCAD Deficiency?
MCAD deficiency is caused by pathogenic variants in the ACADM gene. The condition follows an autosomal recessive inheritance pattern, meaning a child must inherit one altered copy of the gene from each parent to develop the condition.
Parents who each carry one altered copy of the gene are usually healthy themselves. With every pregnancy, two carrier parents have:
- a 25% chance of having a child with MCAD deficiency
- a 50% chance of having a child who is an unaffected carrier
- a 25% chance of having a child who inherits neither altered gene.
Carrier screening can identify couples at increased risk before or during pregnancy.
What Are the Symptoms?
Many infants with MCAD deficiency have no symptoms until they experience a prolonged period without feeding or develop an illness.
Symptoms can include:
- poor feeding
- vomiting
- lethargy or excessive sleepiness
- low blood sugar (hypoglycaemia)
- seizures
- breathing difficulties
- loss of consciousness.
Without prompt treatment, a metabolic crisis can lead to brain injury, liver dysfunction, cardiac complications, or even sudden death.
In many countries, including Australia, MCAD deficiency is included in newborn screening programs, allowing affected babies to be diagnosed before symptoms occur.
How is MCAD Deficiency Managed?
The cornerstone of treatment is avoiding prolonged fasting.
Management typically includes:
- feeding infants regularly, including overnight when necessary
- following age-specific fasting guidelines
- providing extra carbohydrates during illness
- having an emergency management plan if vomiting or poor feeding develops
- seeking urgent medical care during significant illness.
Some individuals may also benefit from dietary advice provided by a metabolic physician and specialist dietitian.
With early diagnosis and careful management, most children with MCAD deficiency grow and develop normally.
The Role of Genetic Testing
Diagnosis is often suggested by newborn screening and confirmed through biochemical testing and genetic testing of the ACADM gene.
Genetic testing can:
- confirm the diagnosis
- identify other family members who may be carriers
- assist with reproductive planning
- enable testing of future pregnancies if desired.
For families with a known diagnosis, genetic counselling provides important information about inheritance, recurrence risks, and available reproductive options.
How Rosalind Genetics Can Help
Learning that your child has an inherited metabolic condition can feel overwhelming. Our experienced genetic counsellors work closely with families to explain the diagnosis, discuss genetic testing results, assess risks for other relatives, and provide support when planning future pregnancies.
We also work collaboratively with your child’s metabolic specialist, paediatrician, and other healthcare providers to ensure families receive coordinated, evidence-based care.
Early Diagnosis Makes All the Difference
Before newborn screening became widespread, MCAD deficiency was often diagnosed only after a child experienced a serious metabolic crisis. Today, early detection and simple preventive measures have transformed the outlook for affected individuals.
If your family has a history of MCAD deficiency, or you have questions about carrier screening, newborn screening results, or genetic testing, the team at Rosalind Genetics is here to help you understand your options and make informed decisions with confidence.
