Methylmalonic acidemia represents a group of disorders that affect the way a person breaks down proteins and fats. In general, symptoms of methylmalonic acidemia can occur from any time between the neonatal period and adulthood. However, the cblA type is usually associated with onset of symptoms in infancy or early childhood. Symptoms often first present as an episode due to infection or other external stressors (metabolic decompensation) and may include vomiting, dehydration, and lethargy. Long-term complications can include low muscle tone (hypotonia), developmental delay and intellectual disability, anorexia and poor growth (failure to thrive), chronic kidney disease, and pancreatitis.
The estimated incidence of methylmalonic acidemia is 1 in 50,000 to 1 in 100,000 people. The portion of methylmalonic acidemia attributed to cblA Type is ~25%.
There is no cure for methylmalonic acidemia. Treatment is divided between managing an acute crisis (metabolic decompensation) and management of symptoms between crises. Metabolic crisis is managed in a hospital and involves increasing the amount of fluid in the body, ensuring proper nutrition (reduced or no protein and increased glucose-intake), and monitoring laboratory work for signs of further complications (like those related to elevated ammonia levels), which is best done by a metabolic expert. Long-term management includes a high-calorie diet that is low in protein, hydroxocobalamin (vitamin B12) intramuscular injections, carnitine and other supplements, and antibiotics. Transplant may become necessary if organ failure occurs.
Methylmalonic acidemia is associated with a number of chronic issues and higher than average mortality rates. Even with treatment, the cblA type can be associated with symptoms, like intellectual disability or kidney disease. In a small percentage of cblA cases, a metabolic crisis can lead to coma and death, especially if the individual is left untreated.
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Explanations of an extensive number of genetic diseases written for the public by the U.S. government's National Institutes of Health.