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MCAD Deficiency: Symptoms, Meaning, Treatment

MCAD deficiency is a rare genetic disease characterized by the body’s inability to use fatty acids as an energy source. Update on symptoms, causes and treatment with Dr. Jean-Baptiste Arnoux, pediatrician specializing in rare diseases.

Definition: what is an MCAD deficiency?

the Medium-Chain-Acyl-CoA-Dehydrogenase deficiency (MCAD) is a rare metabolic disease linked to genetic mutations which lead toinability of the body to use fatty acids as a source of energy. Since the fatty acids are only partially used, an energy deficit occurs in certain organs. This chronic disease generally begins at birth and affects 1/26,000 births (according to data from the first year of screening in France, 2021). “Normally, when we are fasting or when the body needs a lot of energy because we play sports or because we are sick, our adipocytes (fat cells) will naturally release fatty acids in the blood. These fatty acids will be captured by the cells which will use them as a source of energy. In MCAD deficiency, this process that allows cells to use fatty acids is dysfunctional“, develops Dr. Jean-Baptiste Arnoux, pediatrician.

What are the symptoms of MCAD deficiency?

Most patients with an MCAD deficiency will not have never any symptoms of their disease, but they are at risk of having it in certain very specific circumstances. “Symptoms mainly occur in situations of high energy demand such as a fever or prolonged fasting“, indicates the pediatrician specializing in rare diseases. The symptoms can be very severe: a hypoglycaemia, heart rhythm disturbances, liver failure, severe malaise which can leave scars. The organs suffer from not producing enough energy. In the absence of treatment and preventive measures, MCAD deficiency can be life-threatening.

What causes an MCAD deficiency?

MCAD deficiency is a genetic disease linked to an abnormality of the ACADM gene which produces an enzyme called medium-chain acyl-CoA dehydrogenase. “This enzymatic deficit is responsible for a decrease in the production of energy in the cells: the body then finds itself unable to use fat as a source of energy.“, details the specialist.

Since December 1, 2020, the MCAD deficit is detected during neonatal screening (Guthrie test), at the same time as other genetic diseases, from a few drops of blood collected on a blotting board taken at 3 days of life. If the result is normal, the parents will not be contacted. On the other hand, they will be contacted in the event of an anomaly, and referred to a pediatrician specializing in the disease.

It is necessary to avoid that the child is fasting more than 12 to 14H

What is the treatment for MCAD deficiency?

The treatment is mainly based on dietary measures. “If the treatment is followed correctly, the child can lead a normal life. It is important to have meals very regularly during the first year of life, every 3 hours at birth then we gradually expand so that at 12 months, we can allow 12 hours of fasting. Beyond that, parents are asked to try to prevent their children from fasting for more than 12 to 14 hours when all is well. At the end of the neonatal screening, the children are referred to a specialized center (reference center or competence center for hereditary metabolic diseases) where they will be monitored according to a national protocol.“, details Dr. Jean-Baptiste Arnoux. The younger the child, the greater the risk of decompensation. When the child is sick, has a fever (whatever the cause) or eats less well (whatever the cause), it is necessary to bring glucose very regularly , including at night, and in large quantities. It can go through a glucose-enriched drink offered regularly to the child at home, or even by a infusion in hospital if the child is unable to drink (vomiting) or has symptoms of decompensation (hypoglycaemia etc.). The prevention of decompensation by simple dietary measures is at the heart of the concerns.

Thanks to Dr Jean-Baptiste Arnoux, pediatrician at the Reference Center for Hereditary Metabolism Diseases at the Necker-Enfants Malades hospital.

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