MMA is an organic acid disorder. It is a hereditary disease that is caused by a missing or faulty enzyme (methylmalonyl-CoA mutase) needed to convert amino acids into energy. A number of toxic compounds, called organic acids, build up in the blood and cause problems including brain damage and death. There are several types of MMA called mutase deficiency, Cbl A, B, C or D.
The gene defects for MMA are inherited when both parents have the same abnormal gene and unknowingly pass it on to their baby. A parent who has the abnormal gene, but not the disease, is called a carrier. The health of a carrier is rarely affected. However, for each pregnancy of two such carriers, there is a 1 in 4 chance that the child will be born with the disease. MMA occurs in about 1 in every 75,000 births in Australia.
MMA may present with a severe metabolic crisis in the newborn period or later. A less severe presentation is also possible. Problems can include lethargy, failure to thrive, vomiting, dehydration, floppiness, and enlarged liver. The crises may involve drowsiness, coma, and seizures, with subsequent developmental delays.
MMA is usually treated with a low protein diet, plus carnitine medication and sometimes vitamin B12. More intensive treatment is sometimes needed when the child is sick.
The screening test will also detect several other organic acid disorders including: propionic acidaemia, isovaleric acidaemia, glutaric aciduria type I, beta-ketothiolase deficiency, hydroxymethylglutaric aciduria, multiple carboxylase deficiency, and 3-methylcrotonyl-CoA carboxylase deficiency.
These are hereditary diseases that cause problems similar to methylmalonic aciduria. They are also treated in a similar way.
Some of these disorders are very rare and the reliability of their detection is not yet certain. For glutaric aciduria type I, a proportion of patients are "low excretors" and detection may be difficult or impossible.