Introduction 

MCADD is a rare genetic condition where a person has problems breaking down fat to use as an energy source.

This means that someone with MCADD can become very ill if their body's energy demands exceed their energy intake, such as during infections or vomiting illnesses when they're unable to eat.

Problems occur because fat is only partially broken down, which leads to a lack of energy and a build-up of harmful substances in the body

MCADD is a lifelong condition that's present from birth. It's estimated to affect up to 1 in every 8,000 babies born in the UK and is usually picked up using the newborn blood spot test.

The full name for MCADD is medium-chain acyl-CoA dehydrogenase deficiency.

This page covers:

Is MCADD serious?

Symptoms of MCADD

What causes MCADD?

How MCADD is inherited

Screening and testing for MCADD

How MCADD is treated

Information about you

Is MCADD serious?

MCADD is a potentially serious condition that can be life-threatening if not recognised quickly and treated appropriately.

However, most cases are picked up soon after birth and can be managed quite easily (see How MCADD is treated below).

With proper care, there's no reason why someone with MCADD cannot live a normal, healthy and active life.

Symptoms of MCADD

If someone with MCADD becomes unwell and is unable to eat or tolerate food, they may experience the following symptoms:

  • appearing unusually tired and sluggish
  • being sick
  • excessive sweating
  • rapid breathing
  • seizures (fits)

Left untreated, more serious and potentially life-threatening problems can develop, including coma and brain damage.

You'll be given an emergency contact number to call immediately if you or your child has MCADD and experiences symptoms.

If this information isn't easily available, call 999 for an ambulance or go to your nearest accident and emergency (A&E) department and tell them about your or your child's MCADD.

What causes MCADD?

MCADD is caused by a fault in the gene that provides the instructions to make an enzyme called medium-chain acyl-CoA dehydrogenase (MCAD).

This genetic fault causes the enzyme to either not work properly or be missing entirely, which means the body cannot fully break down fat to release energy.

If the body needs to break down fat quickly (for example, if you're unwell and haven't eaten for a while), energy cannot be produced quickly enough to meet the body's needs and substances created when fat is partially broken down can build up to harmful levels in the body.

This can lead to serious problems if not treated quickly.

How MCADD is inherited

A child will only be born with MCADD if they inherit a copy of the faulty gene that causes it from both of their parents.

The parents won't normally have the condition themselves because they usually only have one copy of the faulty gene each. This is known as being a "carrier".

It's estimated that up to 1 in every 40 people in the UK could be carriers of the faulty gene that causes MCADD.

If both parents are carriers of the faulty gene, there's a:

  • 25% chance each child they have will not inherit any faulty genes and won't have MCADD or be able to pass it on
  • 50% chance each child they have will just inherit a copy of the faulty gene from one parent and be a carrier
  • 25% chance each child they have will inherit copies of the faulty gene from both parents and will have MCADD

Read more about genetic inheritance.

Screening and testing for MCADD

newborn blood spot test is now offered to all babies in England to help detect problems, including MCADD early on. 

When your baby is five to eight days old, a health professional will prick their heel and collect drops of blood on a special card. The blood is then sent to a laboratory to be checked for abnormalities that could indicate MCADD.

You should receive the results by the time your baby is six to eight weeks old. You'll be contacted sooner if a problem is found in order to attend a hospital appointment to discuss this further.

The screening result isn't 100% accurate, so further urine and blood tests will be carried out to confirm the diagnosis. You, your partner and any other children you have may also be tested to see if you carry the faulty gene that causes MCADD.

If you've previously had a child with MCADD, the blood spot test should be carried out within 24-48 hours of birth.

How MCADD is treated

There's no specific treatment for MCADD. A specialist care team will give you advice about how to look after your child and support them as they get older.

Children and adults with MCADD can eat a normal diet, as long as they:

  • frequently take special high energy drinks when they're ill – this includes common illnesses such as fever, diarrhoea, or vomiting
  • avoid long periods without eating during the newborn period and infancy even when well – the length of time your child can go without eating is known as the maximum "safe fasting time" and it varies depending on age; you'll be given advice about this

The high energy drinks used in treating MCADD are available on prescription from your GP. You'll be advised by a specialist dietitian about when to use them and how much to use. If the drinks don't help or your child refuses them, they may need to be treated in hospital.

You can find more detailed information about MCADD treatment in the MCADD information sheet for parents and carers (PDF, 116kb) produced by the British Inherited Metabolic Diseases Group (BIMDG).

Information about you

If you or your child have MCADD, your clinical team will pass information about you/them on to the National Congenital Anomaly and Rare Diseases Registration Service (NCARDRS).

This helps scientists look for better ways to prevent and treat this condition. You can opt out of the register at any time.

Find out more about the register.

Support groups

In addition to the support of your care team, you may find it useful to contact a national or local support group for people with MCADD and their families.

One the main groups in the UK is Climb. You can find information about MCADD on its website and you can speak to their Family Advisers for free on 0800 652 3181.

Page last reviewed: 02/02/2016

Next review due: 02/02/2018