High propionylcarnitine may be caused by methylmalonic acidemia, an autosomal recessive disorder that is primarily due to defects in methylmalonyl coenzyme A mutase or defects in the metabolism of its coenzyme cobalamin (vitamin B12). Patients have elevated blood propionylcarnitine levels and propionylcarnitine to acetylcarnitine ratio. Patients with early-onset disease usually start within 1 year of age and may present with convulsions, motor dysfunction, and choreoathetosis, and are often associated with hematologic impairments, such as megaloblastic anemia, and in some cases liver and kidney impairments. Patients with delayed-onset disease usually have symptoms at the age of 4 to 14 years, or even in adulthood, and often suffer from a combination of damage to the spinal cord, peripheral nerves, liver, kidneys, eyes, blood vessels, and skin, etc. In children or adolescents, the disease manifests acute neurological symptoms, such as cognitive decline, blurred consciousness, and intellectual backwardness, or even subacute spinal cord degenerative changes. If high levels of propionylcarnitine are detected in the examination, timely medical consultation should be sought to avoid delaying the condition.