Methylglutaconic Aciduria Type III

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3-methylglutaconic aciduria type III (MGA III) is an autosomal recessive condition and belongs to a group of conditions called organic acidurias. It is characterised by the association of optic degeneration and choreoathetosis with 3-methylglutaconic aciduria. It is believed that MGA III is caused by mutations in the OPA3 gene. The exact mechanisms of this gene still remain to be proved however it is believed that this is the gene that is involved in this mitochondrial disorder condition.

To date, the vast majority of reported cases involved the Iraqi-Jewish population, in which the prevalence of the disorder has been estimated at around 1 in 10, 000.

Symptoms may begin to develop within childhood, within adulthood symptoms are said to stabilise. Some of the signs and symptoms are:

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

Diagnosis may be confirmed up on presentation with early-onset optic atrophy and choreoathetosis and also by detection of an elevation in the levels of 3-methylglutaconic and 3-methylglutaric acid present in the urine. This subtype of MGA can be distinguished from others through detection of mutations in the OPA3 gene through gene testing. This method allows the determination of bloodlines and the genetic diagnosis of vulnerabilities to inherited diseases, this will be explained to you if it is thought that you may have this condition.

Treatment is symptomatic only and should be managed by a multidisciplinary team which may include a doctor, physiotherapist and a dietitian. More information upon this will be given at diagnosis.

MGA III 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 MGA III. 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 MGA III and go on to have further children, their New-born Screening test should be carried out within 24-48 hours of birth.

References are available on request. Please contact us on 0800 652 3181 or by emailing contact@metabolicsupport.org.

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This information about metabolic diseases is provided by Metabolic Support UK and is intended for educational purposes only. It should not be used for diagnostic or treatment purposes.

Should you require more detailed information please contact Metabolic Support UK by email (contact@metabolicsupport.org) or by telephone ( 0800 652 3181). For specific medical information regarding a disorder or individual please contact your GP or Paediatrician. Metabolic Support UK accepts no responsibility for any errors or omissions nor does Metabolic Support UK assume any liability of any kind for the content of any information contained within this summary or any use that you may make of it.