关键词: 左卡尼汀, 肉碱缺乏症, 孤独症谱系障碍, 三甲基赖氨酸羟化酶

Abstract: Autism spectrum disorder is a developmental disability that can cause significant social，communication and behavioral challenges. There are many genetic or  non-genetic causes for multiple types of autism spectrum disorders. Levocarnitine is a water soluble vitamin with the structure similar to amino acid. It plays essential roles in the metabolism with the main function being the transport of long-chain fatty acids from the cytosol to the mitochondrial matrix for β-oxidation. Carnitine deficiency can lead to mental and behavior problems such as autism spectrum disorders. In some patients，multiple organs such as heart，skeletal muscle，brain and liver were injured. Sudden death occurred in severe cases. Carnitine homeostasis normally is maintained through dietary intake，endogenous synthesis，renal excretion and reabsorption. The endogenous synthesis of levocarnitine is completed by four-step enzymatic reactions in mitochondria. Trimethyllysine hydroxylase is a key enzyme in carnitine synthesis. Trimethyllysine hydroxylase deficiency is an X-linked inherited disorder，which causes carnitine synthesis disorder. It is one of the causes of autism spectrum disorders. Early diagnosis and levocarnitine supplementation are the keys to improve the prognosis of patients with autism caused by trimethyllysine hydroxylase deficiency.

Key words: levocarnitine, carnitine deficiency, autism spectrum disorders, trimethyllysine hydroxylase deficiency