Medium-chain acyl-CoA dehydrogenase deficiency (MCADD)

12 min read

What is medium-chain acyl-CoA dehydrogenase deficiency?

Medium-chain acyl-CoA dehydrogenase deficiency (MCADD) is a rare genetic condition in which a person has problems breaking down fatty acids for energy.

This means that if they go for long periods without eating they can experience a range of unpleasant symptoms, such as:

  • feeling very tired and sluggish
  • being sick
  • seizures (fits)

Left untreated MCADD can lead to more serious complications such as

, brain damage and liver failure and can sometime prove fatal.

Symptoms can be triggered once a baby stopped receiving regular nightly feeds. Though there have been a number of cases where symptoms begin shortly after birth due to an interruption in a new-born baby’s feeding.

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symptoms of medium-chain acyl-CoA dehydrogenase deficiency

What causes MCADD?

People with MCADD are born with a faulty or missing enzyme that the body normally uses to break down fatty acids (an enzyme is a type of protein that can cause chemical reactions inside cells).

During long periods between eating, the body breaks down its fat stores to produce energy. Fats are broken down into fatty acids, which are then broken down into shorter and shorter lengths. At each step, energy is released.

Therefore, when people with MCADD go for a long time without eating two harmful effects occur:

  • there is a build-up of medium chain fats inside the body which can have a toxic (poisonous) effect
  • the body then uses its glucose resources as an alternative energy source which can lead to a sudden and severe drop in blood sugar levels (

The faulty or missing enzyme is the result of genetic mutations a child inherits from their parents (the parents themselves are usually unaffected by MCADD).

A genetic mutation is when the instructions found in all living cells becomes scrambled in some way meaning that one or more of the body’s processes does not work properly.

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causes of medium-chain acyl-CoA dehydrogenase deficiency

Treating MCADD

There is currently no cure of MCADD so treatment involves making sure that you or your child doesn’t go for long periods without eating

The maximum ‘safe fasting time’ for children who are not ill can vary according to age:

  • babies under the age of four months should not go more than six hours without eating
  • babies between the aged of 4-8 months should not go more than eight hours without eating
  • babies between the ages of 8-12 months should not go more than ten hours without eating
  • all other children (and adults) over the age of one year should not go more than 12 hours without eating

Sick children will need to be fed more frequently.

If you or your child experiences any symptoms of MCADD, there are a number of high-glucose drinks that can be used to boost blood sugar levels.

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treatment of medium-chain acyl-CoA dehydrogenase deficiency


In the past babies with MCADD went undiagnosed until they experienced symptoms – often known as an acute attack or metabolic crisis.

This could often be life-threatening as the parents had no idea what was happening and how to treat the symptoms.

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diagnosing medium-chain acyl-CoA dehydrogenase deficiency


The outlook for MCADD is usually very good.

The condition is relatively straightforward to manage. Providing that the condition is diagnosed and that dietary recommendations are kept to there is no reason why a child with MCADD cannot live a normal healthy life.

Symptoms of MCADD

Symptoms of medium-chain acyl-CoA dehydrogenase deficiency (MCADD) can occur:

  • after a long period without eating (fasting)
  • during or after a, usually trivial, infection such as the common cold – being ill increases the body’s demand for energy and can also cause loss of appetite

Symptoms of MCADD include:

  • your baby or child appears unusually tired, sluggish and lazy
  • being sick
  • excessive sweating
  • rapid breathing
  • swelling of their liver which may be noticeable to the touch
  • seizures (fits)

Older children and adults may appear unusually nervous and excitable.

Left untreated MCADD can be life threatening. The brain can swell causing brain damage, the liver can stop functioning (liver failure) and a there’s a risk of slipping into a coma.

You will be given an emergency contact number to call immediately should your baby or child starts experiencing the symptoms of MCADD.


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

This is due to a fault in the gene (genetic mutation) that provides instructions for making the enzyme which means that 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 the lack of the MCAD enzyme.

If the body needs to break down fats quickly (for example, if your child hasn’t eaten for a while), 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


The genetics of MCADD

The majority of cases of MCADD are caused by a genetic mutation called 985A>G which 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. In order to develop MCADD a person needs a pair of the mutated genes; 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 1 in 4 chance of having the condition.

If you are an adult with MCADD your children are likely to be unaffected unless you conceive a child with someone who is a carrier of the mutation. In this case, there is a 1 in 2 chance of your child developing MCADD.

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science of genetics

Diagnosing MCADD

Medium-chain acyl-CoA dehydrogenase deficiency (MCADD) is diagnosed by a screening test (blood test) offered to all newborn babies.

During the screening test, the midwife takes blood from your baby's heel. The blood is then checked for abnormalities in the levels and makeup of fats in the blood which occur when the body is unable to break down fatty acids.

If there is any doubt about a diagnosis it can usually be confirmed using a genetic test.

This is done by extracting a sample of DNA from your baby’s blood and then checking the genetic information stored in it for mutations known to cause MCADD such as the 985A>G mutation.

If the diagnosis does prove positive then you will be referred to a specialist so a detailed treatment and diet plan can be drawn up. Read more about

treating medium-chain acyl-CoA dehydrogenase deficiency

Treatment for MCADD

A comprehensive plan will be drawn up for your child by a specialist with experience in treating medium-chain acyl-CoA dehydrogenase deficiency (MCADD).

The plan will cover:

  • how often your child should eat
  • what your child should eat
  • what you should do if your child is not eating normally due to illness or similar – this usually involves giving your child high-glucose drinks which is known as an emergency regimen

You will be given a number of sachets, consisting of glucose and oral rehydration solutions that can be used in an emergency.

As part of this plan you will meet regularly with a dietician so your child’s progress can be tracked and you can discuss any problems or issues. A dietician is a health professional who works with people who have special dietary needs.

Other members of your child’s care team may include:

  • a doctor who specialises in the treatment of children (paediatrician)
  • health visitor
  • a specialist nurse

You will also be given telephone numbers you can use in case of emergency.

The advice regarding diet will change as your child grows older. This is outlined below.

Infants under 1 year

You can feed a newborn baby with MCADD just like any other baby; with breast milk or with normal infant formula; although some types of formula may be unsuitable. Check with your care team.

You should feed your baby every 3-4 hours. The times between feeds is known as fasting.

Your should never let your baby fast for more than six hours even if this means waking them up to feed them, until they reach the age of four months.

After that time:

  • babies between the aged of 4-8 months should not fast for more than eight hours
  • babies between the ages of 8-12 months should not fast for more than ten hours

Weaning a baby with MCADD (introducing solid food into their diet) is done in exactly the same way as with any other baby.

The only food that your child should avoid eating is coconut as coconuts contain large amounts of fatty acids and your child would be unable to digest them.

What to do if your baby is unwell

If your baby becomes unwell and starts refusing feeds you should first contact your care team for advice.

They will usually advise you to make up an emergency regimen consisting of a sachet of glucose mixed with 200ml of cooled boiled water.

If your child is also experiencing symptoms of diarrhoea and /or being sick (vomiting) you should make up a similar regimen consisting of 200ml of water and a combination of glucose and oral rehydration solution.

The fluid can then be poured into a bottle or cup; depending on what your baby finds easier.

Your dietician will provide more detailed instructions as well as information sheets.

The recommended fluid intake is:

  • age 0-3 months - 80ml every 2 hours or 70-120ml every 3 hours day and night
  • age 4-6 months - 85-100 ml every 2 hours or 130-150ml every 3 hours day and night
  • age 7-9 months - 90-100ml every 2 hours or 130-150ml every 3 hours day and night
  • age 10-12 months - 100ml every 2 hours or 150ml every 3 hours day and night

You should contact your care team for further advice if your baby:

  • is experiencing persistent diarrhoea and /or vomiting
  • is unable or unwilling to take the recommended fluid intake
  • is breastfed and will not accept fluid from a bottle or cup
  • has not resumed normal feeds within 48 hours

Older children

Older children should be encouraged to eat three meals a day; breakfast, lunch and dinner.

Snacks between meals are not usually recommended unless your child has a poor appetite.

If snacks are required they should be given at regular intervals to prevent constant snacking (grazing) which could affect appetite.

It is usually safe for your child to sleep through the night without needing to be fed provided that they eat something small before going to bed, such as milk and cereal or toast.

Your child should eat breakfast soon after waking. If they refuse breakfast a sugary drink (see below) can be given as an alternative, with a mid morning snack before lunch. However, this should not be encouraged on a regular basis.

You should never let a child over the age of one fast for more than 12 hours.

What to do if your child is unwell

You will need to give them an emergency regime as above.

Alternatively you can give them commercially available sugary drinks that contain high amounts of glucose. These include:

  • Fruit Shoots
  • J20
  • a carton of Ribena (the original type not the sugar reduced or sugar free types)
  • Lucozade energy (but not the sport variety as that does not contain enough glucose)
  • fizzy drinks such as Coca Cola, Pepsis, 7UP, etc (again make sure that they are not sugar-free or diet versions)

The long-term use of these types of sugary drinks is not encouraged as they can cause health problems in later life such as

tooth decay

The recommended fluid intake is:

  • aged 1-3 years – 100ml every two hours
  • aged 3-4 years –110-120ml every two hours
  • aged 5-6 years – 125-135ml every two hours
  • aged 7-8 years – 145ml every two hours
  • aged 9-10 years - 150ml every two hours
  • aged 11-13 years - 165ml every two hours
  • aged 14-15 years - 185ml every two hours
  • aged 16 years and above - 200 ml every two hours

Contact your care team for advice if your child refuses the fluid or is unable to keep it down.

Advice for adults with MCADD

There are a number of issues that adults with MCADD need to be aware of. These are discussed below.


Heavy alcohol consumption, especially binge drinking (drinking large amounts of alcohol in a short-space of time) can be dangerous if you have MCADD for a number of reasons:

  • people often pass out after binge drinking so the time before eating your next meal could become dangerously delayed
  • alcohol can cause your blood sugar levels to drop which can trigger the symptoms of MCADD

If you do choose to drink alcohol, drink in moderation and never on an empty stomach.

Weight management

If you are trying to lose weight you should discuss the safest way to do this with your care team.

It is especially important to avoid fad or crash diets as a sudden change in the amount and type of food that you eat could trigger the onset of symptoms.

Important: Our website provides useful information but is not a substitute for medical advice. You should always seek the advice of your doctor when making decisions about your health.