Measurement of methylmalonic acid in the urine is used for laboratory testing of children with signs and symptoms of methylmalonic acidemia and for evaluating patients with signs and symptoms related to cobalamin deficiency (vitamin B12).
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Elevated levels of methylmalonic acid (MMA) in the serum blood and urine occur when there is a disturbance of the enzymes active in the metabolic pathway. Increased methylmalonic acid in the blood is a rare inherited, autosomal recessive disorder that causes methylmalonic acid metabolism to fail. One specific genetic mutation, 271dupA, represents 40% of the pathological alleles of the disease. The disease includes symptoms such as nausea, vomiting, progressive encephalopathy, convulsions, and developmental delays. If the disease is not detected early, the condition worsens as the infant consumes more protein. This leads to acidemia, hyperammonemia, coma, and death. If the disease is diagnosed early, acidemia can be minimized by a low-protein diet. As this condition is infrequent, many infants can die from the disease without being diagnosed.
Methylmalonic acid is also a sensitive indicator of vitamin B12 deficiency, as with pernicious anemia. Measuring methylmalonic acid and determining vitamin B12 is the first step in controlling pernicious anemia. If both measurements are elevated, the follow-up includes screening for endogenous antibodies, parietal cell antibodies (APCA), and gastrin levels measurement.
Acquired nutritional deficiencies are much more common than genetic abnormalities and may be due to intestinal malabsorption, reduced digestion, or poor nutrition. Elderly patients with cobalamin deficiency may develop peripheral neuropathy, ataxia, loss of balance and vibration sensation, memory impairment, depression, and dementia, even without anemia. Other conditions such as kidney failure, hypokalaemia, and small intestine bacterial overgrowth also contribute to possible causes of mild methylmalonic acidemia and aciduria.
Several studies have shown that determining methylmalonic acid in serum or urine may be a more reliable indicator of cobalamin deficiency than the immediate determination of cobalamin.
Possible Interpretations of Pathological Values
- Increase: Hereditary disorder (methylmalonic acidemia), pernicious anemia, low B12 levels
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