Autism spectrum disorder (ASD) is used to describe individuals with a specific combination of disorders in social communication and repetitive behaviors, highly restricted interests, and/or sensory behavior that begin early in life. The prevalence of ASD has been increasing rapidly in recent years. Pathophysiology of ASDs remains still unclear; however, genetic defects and multifactorial causes have been reported to play an important role in genetic disorders. The prevalence of inborn errors of metabolism (IEM) reported among patients with ASD is 2-5%. The clinical presentation of congenital disorders of glycosylation (CDG) may be in the form of psychiatric disorder only.