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Medium-chain acyl-CoA dehydrogenase deficiency (MCADD)

Medium-chain acyl-CoA dehydrogenase deficiency (MCADD) is an inherited condition.

People with MCADD cannot break down fats from their food quickly enough to make energy when they are sick.

This is important if they:

  • have a fever
  • have diarrhoea
  • are vomiting
  • are fasting

This is because an enzyme is either missing or not working properly. This can cause toxins and low blood glucose (sugar) to build up.

MCADD can cause serious complications, such as brain damage, coma or even death if it is not treated.

Babies born in Ireland with MCADD

Around 1 in every 66,000 babies born in Ireland has MCADD.

Babies with MCADD inherit 1 altered gene from each parent.

How heel prick screening can help

If the heel prick suggests your baby may have MCADD, they will see a specialist.

If their treatment starts early, your baby can have a healthy and active life. They can avoid the complications of MCADD.

Newborn babies can sometimes become sick and show symptoms of MCADD before they have their heel prick screen or their results. This is very rare.


If your baby has MCADD, they can eat a normal diet.

They will also need to take special high energy drinks when they're ill. This includes common illnesses such as fever, diarrhoea, or vomiting.

They should also avoid long periods without feeding while they are under 1 year old.

The length of time your child can go without eating depends on their age. It is called the 'maximum safe fasting time'.

Non-urgent advice: Contact your GP if your newborn baby has any symptoms of MCADD:

  • drowsiness
  • poor feeding
  • vomiting
  • low energy
  • seizures

Page last reviewed: 12 December 2022
Next review due: 12 December 2025