Methylmalonic acidemia is an inherited disorder in which the body is unable to process certain proteins and fats (lipids) properly. The effects of methylmalonic acidemia vary from mild to life-threatening. This condition, which usually appears in early infancy, is characterized by vomiting, dehydration, weak muscle tone (hypotonia), and excessive tiredness (lethargy). Without treatment, the disorder can lead to coma and death in some cases.