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Methionine adenosyltransferase deficiency is a very rare metabolic disorder resulting in an isolated increase of the amino acid methionine in the blood (hypermethioninemia). In most cases there are no symptoms and it is usually a benign condition, but some patients may present with neurologic or developmental problems and/or bad breath. It is caused by mutations in the MAT1A gene. Inheritance is autosomal recessive. When needed, treatment is with a diet restricting methionine. S-adenosylmethionine (SAMe) supplementation may also be useful.
Source: GARD Last updated on 05-01-20
The disease is considered benign in many cases and most patients only have isolated hypermethioninemia. However, about 50% of patients with mutations in the MAT1A gene have developed neurological symptoms later in life, so it cannot be considered to be a benign genetic disorder for all patients. Symptoms that have been described include:
Neurological abnormalities are more common when methionine levels in the blood are above 800 μmol/L and rare in people with lower levels. Brain images may show some changes, such as inflammation and demyelination, especially in patients with neurological problems.
Hypermethioninemia can also be associated with an unusual breath odor likely due to formation of a substance known as dimethylsulfide that results from the problem with the enzyme deficiency.
Liver function tests in patients have been normal so far.
Methionine adenosyltransferase deficiency is the most common cause of persistent isolated hypermethioninemia and should be suspected in people with unexplained hypermethioninemia. Also, when a patient has unexplained neurological signs and symptoms, disorders of methylation should be investigated at least by analysis of plasma amino acids.
Last updated on 05-01-20
All patients, even when they do not have any symptoms, should have regular neurological and cognitive testing due to the possibility of neurological symptoms. If indicated, a brain MRI could also be done. Symptomatic patients should be treated with a methionine restricted diet if the methionine level is above 600 μmol/L. Treatment aims to get the methionine levels around 500 to 600 μmol/L. Neurological symptoms are more likely to develop when methionine levels in the blood are around 800 μmol/L.
S-adenosylmethionine (SAMe) supplementation (AdoMet supplementation) may be indicated if clinical signs and symptoms develop while on methionine restriction. The most effective oral dose of AdoMet is unknown. Doses between 400 to 1600 mg/day have been used in various conditions and seem to be well tolerated. Some evidence suggests that AdoMet supplementation may lead to normalization of brain changes seen on imaging.
Last updated on 05-01-20
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