Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency is an inherited metabolic disorder in which the body cannot properly break down medium-chain fats to use for energy. It affects roughly 1 in 15,000 to 20,000 newborns. It is screened for because a child can appear completely healthy and then become seriously ill during fasting or illness, and simple preventive steps avoid that risk once the condition is known.
What causes MCAD deficiency
MCAD deficiency is caused by changes (variants) in the ACADM gene, which provides instructions for an enzyme needed to convert certain fats into energy. When that enzyme does not work, the body cannot switch to burning fat when sugar runs low. It is inherited in an autosomal recessive pattern, so a child inherits a variant from each parent.
How newborn screening detects it
MCAD deficiency is detected through the blood-spot screen using tandem mass spectrometry, which measures a pattern of molecules called acylcarnitines. A characteristic pattern flags possible MCAD deficiency and leads to confirmatory testing. The addition of tandem mass spectrometry to newborn screening is a major reason conditions like this are now caught early.
How MCAD deficiency is managed
There is no cure, but management is simple and highly effective: avoid long periods without eating, especially during infancy and during illness, and follow an emergency plan for sick days that ensures the child gets enough sugar. With this approach, most children with MCAD deficiency grow and develop normally. The danger comes almost entirely from undetected cases.
How genetic screening fits in
State newborn screening does an excellent job of catching MCAD deficiency. Genetic screening looks at the same picture from the DNA level and, in a single test, can also assess the genes tied to more than 1,000 other clinically actionable childhood conditions, many of which are not on any state panel. Fore Genomics offers an at-home cheek-swab screen, sequenced in CLIA-certified and CAP-accredited labs, with results supported by board-certified genetic counselors. See how your state’s panel compares, see what we screen for, or start screening.
Frequently asked questions
Is MCAD deficiency on every state panel?
Yes. MCAD deficiency is a core condition on every U.S. state newborn screening panel.
Why does fasting matter with MCAD deficiency?
Children with MCAD deficiency cannot safely rely on burning fat for energy, so going too long without food, especially when ill, can trigger a dangerous drop in blood sugar. Avoiding fasting prevents this.
Is MCAD deficiency inherited?
Yes. It is autosomal recessive, so a child inherits an ACADM gene variant from each parent, who are usually unaffected carriers.
Medically reviewed by Fore’s Clinical Team. This article is for general educational purposes and is not medical advice. Sources: HRSA Newborn Screening; National Organization for Rare Disorders (NORD).