Methylmalonic Acidaemia

What else is it called?

  • MMA 

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What causes it?

Methylmalonic Acidaemia (MMA) is a rare inherited metabolic disorder.  

MMA affects the way you break down protein. Many foods contain protein. The body needs protein for growth and repair. Protein is broken down into amino acids (building blocks of protein) by enzymes (which are like chemical scissors). Enzymes then further break the amino acids into smaller parts. 

In MMA, the body lacks an enzyme called methylmalonyl-CoA mutase. This means the body is unable to break down four amino acids (protein). As a result, there is a build-up of a chemical called methylmalonic acid.  This causes too much methylmalonic acid and other chemicals in the blood and urine. 

Methylmalonic acid also comes from gut bacteria and the breakdown of fatty acids. The body will use these for energy when it has gone a long time without food 

The build-up of harmful chemicals can damage the brain and kidneys and cause problems with other organs. It may cause delays to normal development like walking and talking. 

If the body does not receive enough food e.g. during illness or the body has gone without food for too long, there may be a shortage of energy supply. This causes catabolism which is a break-down of body protein and can lead to a metabolic crisis. 

How common is it?

Generally it is thought the that MMA may affect between 1 in every 50,000 and 1 in every 100,000 In some populations, this can be as high has between 1 in every 25,000 to 1 in every 48,000. 

What are the signs and symptoms?

Some babies with MMA become ill in the first few days of life. Symptoms include: 

  • poor feeding 
  • vomiting 
  • dehydration (lack of body fluids) 
  • floppy baby 
  • excessively sleepy 
  • rapid breathing 
  • seizures 

In a metabolic crisis there is a build-up of methylmalonic acid and other toxic chemicals such as ammonia. It is usually triggered by childhood illnesses e.g. vomiting and diarrhoea, fasting for too long or not having enough energy from food. There should be no delay in treatment. Avoidance of a metabolic crisis is essential 

The effects of MMA quickly become life-threatening if untreated. 

How is it diagnosed?

MMA is diagnosed by measuring high levels of methylmalonic acid and other chemicals in the blood and urine. It can also be diagnosed by looking at enzyme levels and at the body’s genes. 

Can it be treated?

In MMA, it is important that enough protein is given for growth…but not too much as toxic chemicals will be made. MMA is managed with the following: 

  • A protein restricted diet 
  • Ensuring a sufficient energy supply 
  • A generous fluid intake 
  • Regular feeding 
  • Carnitine medication 
  • Other medications may be necessary 

Tube feeding may be necessary to give regular feeds. This will ensure energy, nutrient and fluid needs are met and can help to reduce the production of abnormal chemicals. 

During any childhood illness, an emergency regimen is given. This is to avoid a lack of energy supply and build-up of harmful chemicals that cause a metabolic crisis. 

  • Stop all protein in food & drink 
  • Start the emergency regimen. This is made up of glucose polymer 
  • Continue medication as prescribed 
  • Always take full amounts of emergency feeds as prescribed 
  • If symptoms continue and/or you are worried, go immediately to the hospital 
  • Regularly update your metabolic team. 

It is imperative that emergency feeds are started promptly and there are no delays in management. 

MMA is monitored by frequent blood tests to check amino acids, nutrient and chemical levels, height and weight checks and developmental checks. Diet and medications are adjusted according to age, weight and blood chemical levels.  

MMA is a serious inherited metabolic disorder that can lead to severe problems. 

The condition is managed with a protein restricted diet, regular feeding, a generous fluid intake and medications.  

Remember, during illness, it is imperative that emergency feeds are started promptly, followed strictly and there are no delays in treatment. 

Helpful hints: 

  • Always ensure you have a good supply of your dietary products and medicines and that they are in date. 
  • Your dietary products and medications are prescribed. 
  • These are obtained via a pharmacy or home delivery. 
  • Always ensure you have your emergency feed products and a written emergency plan. 
  • Medications to control fever should be given as normally recommended – always keep supplies available. 

Do my family need to be tested?

Humans have chromosomes composed of DNA. Genes are pieces of DNA that carry the genetic instruction. Each chromosome may have several thousand genes. 

The word mutation means a change or error in the genetic instruction. 

We inherit particular chromosomes from the egg of the mother and sperm of the father. 

The genes on those chromosomes carry the instruction that determines characteristics, which are a combination of the parents. 

MMA is an inherited condition. There is nothing that could have been done to prevent your baby from having MMA. 

Everyone has a pair of genes that make the methylmalonyl-CoA mutase enzyme. In children with MMA, neither of these genes works correctly. These children inherit one non-working MMA gene from each parent 

Parents of children with MMA are carriers of the condition. Carriers do not have MMA because the other gene of this pair is working correctly. 

When both parents are carriers, in each pregnancy the risk to the baby is as follows: 

  • 25% chance (1 in 4) of MMA 
  • 50% chance (1 in 2) for the baby to be a carrier of MMA 
  • 25% chance (1 in 4) for the baby to have two working genes and neither have MMA or be a carrier 

Relevant Organisations


References are available on request. Please contact Helen Morris by phoning 0845 241 2173 or emailing [Resource Library No: MAP016]. 

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