Let's talk aboutMCAD Deficiency

What is MCAD deficiency? 

MCAD Deficiency is a rare genetic disorder characterized by episodes of very low blood sugar while fasting or under stress. A person must have two variants in the ACADM gene in order to have this genetic condition. People with just one variant in the ACADM gene are called carriers. They’re not expected to have MCAD deficiency themselves, but they could pass their variant on to their future children.

The genetics behind MCAD deficiency

MCAD deficiency is caused by variants (differences) in the ACADM gene. The ACADM gene contains instructions for making an enzyme called medium-chain acyl-CoA dehydrogenase (MCAD). This enzyme helps the body make energy from a particular kind of fat (called medium-chain fatty acids). Certain variants in the ACADM gene disrupt this function, resulting in low energy and a buildup of fatty acids. 

The ACADM gene is shown located on chromosome 1.

Symptoms of MCAD Deficiency

Symptoms of MCAD deficiency typically develop during infancy. Typical signs and symptoms include severely low blood sugar, fatigue, vomiting, seizures, and liver problems.

Did you know?

MCAD deficiency is most common in people of Northern European descent. 

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The 23andMe MCAD Deficiency Carrier Status report* can tell you whether you may be a carrier for MCAD deficiency. Being a carrier means you have a genetic variant that you could pass down to your future children. 23andMe tests for four variants in the ACADM gene linked to MCAD deficiency, and the report is most relevant for people of European descent. 23andMe does not test for all possible genetic variants linked to MCAD deficiency, and individuals who have zero variants detected still have a chance of being a carrier for MCAD deficiency. 

The MCAD Deficiency Carrier Status report is included in the 23andMe Health + Ancestry Service.

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*The 23andMe PGS test uses qualitative genotyping to detect select clinically relevant variants in the genomic DNA of adults for the purpose of reporting carrier status and reporting and interpreting genetic health risks. The relevance of each report may vary based on ethnicity. Our carrier status reports can be used to determine carrier status, but cannot determine if you have two copies of any genetic variant. These carrier reports are not intended to tell you anything about your risk for developing a disease in the future or anything about the health of your fetus, or your newborn child’s risk of developing a particular disease later in life. For certain conditions, we provide a single report that includes information on both carrier status and genetic health risk. The MCAD Deficiency Carrier Status report is indicated for the detection of four variants in the ACADM gene and is most relevant for people of European descent. For important information and limitations regarding carrier status reports, visit  https://www.23andme.com/test-info/.


Merritt JL et al. (2000). “Medium-Chain Acyl-Coenzyme A Dehydrogenase Deficiency.” [Accessed Dec 8, 2021]. 

MedlinePlus. “Medium-chain acyl-CoA dehydrogenase deficiency.” Retrieved Apr 7, 2021, from https://medlineplus.gov/genetics/condition/medium-chain-acyl-coa-dehydrogenase-deficiency/. 

National Organization for Rare Disorders. “Medium Chain Acyl CoA Dehydrogenase Deficiency.” Retrieved Apr 7, 2021, from https://rarediseases.org/rare-diseases/medium-chain-acyl-coa-dehydrogenase-deficiency/.