MCADD - Causes of MCADD

Medium-chain acyl-CoA dehydrogenase deficiency (MCADD) occurs when an enzyme called medium-chain acyl-CoA dehydrogenase (MCAD) is either missing or does not work properly.

This is due to a fault in the gene that provides instructions for making the enzyme. If this happens, the body cannot break down stored fat to release energy.

Fats are normally broken down into fatty acids, which are then broken down into shorter and shorter lengths, with each step producing energy. If your child has MCADD, there is a build-up of medium-length chains due to a MCAD enzyme deficiency.

If the body needs to break down fats quickly (for example, if your child hasn't eaten for a while or is unwell), this build-up of medium-chain fats can become toxic, leading to serious, even life-threatening, symptoms.

In cases of MCADD, the body relies on glucose (a type of sugar in the blood) to produce energy. If someone isn’t eating properly or they are ill, their glucose may be all used up and their blood sugar levels will drop to a dangerously low level, which is known as hypoglycaemia.

The genetics of MCADD

Most cases of MCADD are caused by a genetic mutation called 985A>G. This is thought to be present in around 1 in every 125 people in Europe (the figure may be different in other parts of the world).

Genes come in pairs. You receive one copy of a gene from your mother and one copy from your father. A person needs a pair of the mutated genes to develop MCADD – one from their mother and one from their father.

Usually, a child with MCADD has parents who are unaffected by the condition, but both have a single mutated gene.

This means that the children of two parents "carrying" the 985A>G gene mutation have a 25% chance of inheriting the condition.

If you are an adult with MCADD, your children are unlikely to be affected unless you conceive a child with someone who is also a carrier of the mutation. If this happens, there is a 50% chance of your child developing MCADD.

Read more about the science of genetics.