Methylglutaconic Aciduria Type I

What else is it called?

  • MGA1

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What causes it?

MGA1 is an autosomal recessive condition which belongs to a group of 5 different conditions of the 3-methylglutaconyl aciduria, all of which effect the body’s mitochondria which is the energy producing organelle of the cell.

MGA1 is caused by mutations in the AUH gene which encodes the enzyme 3-methylglutaconyl-CoA hydratase, which is involved in the breakdown of the amino acid leucine. Failure to break down this amino acid can result in the build-up of potentially harmful bioproducts within the body and may cause an array of health risks.

How common is it?

To date, there has been reports of less than 20 people diagnosed with this condition worldwide. Due to the rarity of this condition it is difficult to state whether there is greater chance of males or females being diagnosed with this condition and also which ethnicity it may be more prominent in.

What are the signs and symptoms?

Symptoms of this condition may become apparent from the neonatal period of infancy; however, a diagnosis may not be made until childhood due to the similarity of symptoms to other metabolic conditions, below are a list of more common symptoms you may expect to see with this condition:

  • Delayed speech
  • Failure to thrive
  • Vomiting
  • Muscle degradation of basal ganglia
  • Severe hypertonia [muscle tightness]
  • Progressive neurological defects

Signs and symptoms generally vary and are dependant to the extent to which the amino acid levels are elevated, whilst some people may experience the lesser side effects such as vomiting others may experience the more harmful symptoms such as progressive neurological defects.

How is it diagnosed?

Clinical diagnosis can be made via blood analysis by a blood test or by urinalysis from a 24-hour urine collection or random 1 off urine sample. Individuals diagnosed with 3-MGA type I can be distinguished from those with other forms of 3-MGA [types II, III and IV]by the distinctive pattern of metabolite excretion. With this form of the metabolic condition, levels are highly elevated above the norm, whereas with the other subgroups of the condition they tend to be only slightly elevated.

In some cases, diagnosis may be made prenatally from the detection of high levels of 3-hydroxyisovaleric acid in the amniotic fluid which is fluid where inside the mother’s womb where the baby normally develops.

In some countries the new born screening test for this metabolic condition may be available, this involves a heel prick test from your babies heel approximately 6-8 weeks after birth to test for different conditions, this is more likely to be tested if this condition is present within your family history.

Can it be treated?

Treatment for MGA1 is largely aimed at being symptomatic such as managing vomiting with anti-sickness medication, but dietary management with a modest leucine restriction and supplementation with L-carnitine has found to be beneficial in previous research.

Do my family need to be tested?

MGA1 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 inheritedMGA1. 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 MGA1 and go on to have further children, their New-born 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: AAP002].

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