Organic Acidaemias

Methylmalonic Aciduria (MMA)


Methylmalonic Aciduria (MMA) is an autosomal recessive metabolic disorder where the body is unable to process certain proteins and fats properly. The methylmalonic acidemias are organic acidemias caused by an enzymatic defect in the metabolism of four amino acids (methionine, threonine, isoleucine and valine). This results in an abnormally high level of acid in the blood (academia) and body tissues. The severity of symptoms varies widely, ranging from mild neurological disturbances to metabolic crisis.


The condition is diagnosed during newborn screening via the heel prick test taken 48-72 hours after birth.


1:50,000 – 100,000 estimated worldwide.


Treatment of methylmalonic acidaemia involves dietary modification to restrict the intake of isoleucine, valine, threonine and methionine and a supplement with lysine-free, low-tryptophan amino acid mixtures to ensure supply of the other amino acids essential for optimal health. During periods of illness, fasting and infection, aggressive treatment is initiated to prevent the body breaking down its own energy stores. This comprises limiting protein intake, giving glucose and additional fluids, increasing carnitine supplementation plus, in some cases, using dialysis to reduce ammonia levels and correct metabolic acidosis. Vitamin B12 supplementation helps to improve metabolic control and reduce the risk of complications in those with a deficiency in this co-factor. Long periods of fasting are advised to be avoided.

Support Links & Materials

Organic Acidurias Handbook

OA Fruit and Veg Counting Lists

OA General Protein Counting Lists