Medium Chain acyl-CoA Dehydrogenase Deficiency

What else is it called?

  • MCADD 

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What causes it?

This condition is grouped with the defects known as Fatty Acid Oxidation Disorders (FOD’s). Fat or adipose tissue is the main energy store of our bodies. It is derived not only from the fat that you eat, but also made in the body from any excess calories obtained from your food and drink. When fat is broken down it releases fatty acids. When you eat, regular carbohydrate containing meals, your body uses the sugar in the meals as an energy source and does not use much fat.  

When your body needs more energy, it needs to break down fat quickly. This happens especially if you are ill or if you go without food for a long time. In MCADD, the fat is only partially broken down and therefore your body can not make enough energy quick enough for your body to use it. This leads to a lack of energy and a build up of toxic substances in your body which come from the partially broken down fat. 

How common is it?

MCADD affects up to 1:8,000 babies born in the UK. Newborn Screening detects approximately 60 cases each year in the UK. 1 in 50 in the UK are carriers for the condition and do not show symptoms. 

What are the signs and symptoms?

If you have MCADD you can be perfectly well providing you can eat regular meals or feeds as appropriate for your age. You can take part in all the activities that people of your age can usually undertake, and you will grow and develop normally.  

However, symptoms may develop if you don’t eat regular meals. E.g. leaving long periods without food, or if you are unwell with any illness or infection which stops you tolerating food.  

If you do not know that your child has MCADD, symptoms may occur when they are unwell with an infection. This is usually between 3 to 18 months of age, as they experience an infection for the first time. Occasionally MCADD may present soon after birth or in older infants and exceptionally in adults after long periods without food or during illness.  

Symptoms generally occur as recurrent episodes which are called metabolic crises. These are often triggered by an infection, and/or long period without food.  The crises lead to low blood sugar levels usually with low or absent blood and urine ketones.   

Symptoms of these crises may include: 

  • Unusual or extreme tiredness, feeling sluggish and no energy 
  • Being sick 
  • Excessive sweating 
  • Abnormal breathing 
  • Seizures/fits 

However, the crises tend to vary between individuals both in symptoms and severity.  

Symptoms can begin suddenly and progress quickly becoming severe and life-threatening. This is especially dangerous if you do not know about the condition. MCADD can cause coma and/or death if not treated quickly, although severe problems are rarer in children older than 5 years. The addition of MCADD to the Newborn Screening Programme in the UK helps to prevent this from happening. 

How is it diagnosed?

MCADD is part of the Newborn Screening Programme which is offered to all babies in the UK. When your baby is 5 to 8 days old, a spot of blood will be taken from your baby’s heel. The healthcare professional may call this a heel-prick test. This blood sample will be sent to check if your baby has MCADD. You will receive results within 7-8 weeks, although you will be contacted sooner if the test comes back suggesting your baby has MCADD.  

Not all screening results are accurate, so blood and urine tests will also be carried out to confirm the diagnosis. 

Can it be treated?

There is no cure for MCADD. It is a lifelong condition. However, once you know that you or your baby has the condition, it is manageable. The aim of treatment is to prevent and control the acute metabolic crisis.   

  • Avoid long periods without food. It is dangerous and therefore frequent intakes of food are required. However, when well, a normal infant feeding pattern, or regular healthy eating meals with a good starch intake, is all that is needed. The pattern of feeding in breast fed babies is very appropriate for an MCADD baby.  
  • Follow your emergency regimen – when you receive your diagnosis you will be given an emergency regimen explaining what to do if you or your child becomes ill. This includes getting bugs such as vomiting, diarrhoea and fever. Glucose polymer (energy rich drinks) are given regularly during the illness. The most common of these are Maxijul, Polycal or SOS which are all available on prescription and you will be given advice on how to use them. If you are unable to tolerate these drinks, continue to be ill and/or develop diarrhoea then you will need to be admitted to hospital to be given a glucose/dextrose drip as soon as possible. You will be given an emergency contact number to ring, however if this is unavailable call 999 for an ambulance or go to your nearest hospital’s accident and emergency (A&E) for treatment. 

Once this disorder has been diagnosed and appropriate treatment given the prognosis is extremely good. Children will develop entirely normally and can participate in all the activities appropriate for their age.  

Do my family need to be tested?

MCADD can only be passed on to a child if both parents have a copy of the faulty gene. This is called autosomal recessive inheritance. A person who has a copy of the faulty gene is known as a carrier. 

If both parents are carriers, their child has a one in four (25%) chance of inheriting the disorder, and a one in two chance (50%) of being a carrier. This is the same for each child the parents have. 

If the child only inherits one copy of the faulty gene, they will be a carrier but will not have the disorder. In some rare cases, carriers have had mild symptoms of the disorder for which they carry the faulty gene.  

Once you are diagnosed, you can speak to a genetic counsellor. They can explain how you may have inherited MCADD. They can also tell you about genetic testing for the rest of your family. They can provide advice and support if you go on to have children of your own. 

If you have previously had a child with MCADD and go on to have further children, their Newborn Screening test should be carried out within 24-48 hours of birth. 

Relevant Organisations


References are available on request. Please contact Helen Morris by phoning 0845 241 2173 or emailing [Resource Library No: MFKB01]. 

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