The manifestations of methylmalonic acidemia are varied and complex, and may include vomiting, impaired consciousness, and in severe cases, anemia and hematopoiesis. Methylmalonic acidemia is the most common organic acid metabolism disease in China, which often appears in children. The clinical manifestations of children often lack specificity, and are categorized into early onset and late onset according to the time of onset. 1. Early onset: 1/3 of the early-onset children within 1 year of age develop in the neonatal period, mainly manifested by feeding difficulties, vomiting, physical developmental backwardness, intellectual and motor backwardness, impaired consciousness, hypotonia, epilepsy, etc. In severe cases, respiratory difficulties, hyperammonemia, anemia, metabolic acidosis, hematocrit, coma, etc., and the morbidity and mortality rate is high. 2. Late-onset: the disease can develop in early childhood to adulthood, and the triggers of the first metabolic crisis are often hunger, infection, vaccination, fatigue and other stress factors, or high-protein diets and medications. If the diagnosis and treatment are not timely, it can lead to brain multi-organ failure and damage, often leaving different degrees of neurological abnormalities, such as intellectual and motor disabilities, cerebral palsy, epilepsy. It can be combined with other organ damage, such as renal tubular acidosis, renal insufficiency, recurrent pancreatitis, visual impairment, cardiomyopathy, and bone marrow suppression. Suspicion of methylmalonic acidemia requires prompt hospitalization.