Medium Chain Acyl-CoA Dehydrogenase Deficiency


Fat oxidation is the process by which fatty acids are broken down to release energy and during times of fasting (where no food is eaten) it provides up to 80 per cent of the body’s energy needs. Fat is a key energy source, but the brain cannot use it directly as a fuel and needs to convert it first to ketones in the liver. Medium chain acyl-CoA dehydrogenase deficiency (MCADD) is a rare inherited disorder where the body cannot metabolise (break down) fat properly. It is the commonest fat oxidation defect affecting 1 in 10,000 in the UK population.


Medical text written January 2020 by Dr Mike Champion, Consultant in Paediatric Inherited Metabolic Disease, Evelina Children’s Hospital, Guy’s and St Thomas’ NHS Foundation Trust, London UK.

What are the symptoms?

Patients with MCADD are healthy most of the time. However, infections or prolonged fasting can lead to hypoglycaemia (low blood glucose), drowsiness, coma or death.

How is it diagnosed?

In the UK, infants with MCADD are detected on newborn screening and commenced on treatment prior to the development of symptoms. Further information is available from the National Newborn Screening Programme Centre website.

If an infant has difficulty feeding in the first days of life, symptoms can develop before screening occurs. In infants and children presenting with symptoms, the diagnosis is suggested by low glucose in the blood with a poor ketone response (hypoketotic hypoglycaemia). The diagnosis is confirmed with blood tests for acylcarnitines, which demonstrates the level of partially broken down fat in the blood, tests to identify the genetic mutation responsible for MCADD and a urine test to identify organic acids.

How is it treated?

The main focus of treatment is to prevent low blood sugar developing by avoiding prolonged fasting (eg by making sure that meals are eaten frequently). This is usually only a problem during times of illness such as coughs, colds and tummy upsets. If food cannot be taken due to illness, regular glucose supplements, such as glucose polymer, must be given to the child by mouth. If there is vomiting, bad diarrhoea, refusal to take the glucose supplements or the condition of the child is getting worse, admission to hospital for intravenous glucose (given through a vein) is needed until normal feeding can be reintroduced.

Inheritance patterns and prenatal diagnosis

Inheritance patterns

Autosomal recessive. Genetic advice is available for families with the condition.

Prenatal diagnosis
Prenatal diagnosis is available.

Is there support?

Information and support in the UK for medium chain acyl-CoA dehydrogenase deficiency is available from Metabolic Support UK (see entry Inherited Metabolic diseases).

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