Abstract: The present invention relates to a composition for preventing, improving, or treating fragile X syndrome, fragile X syndrome-related developmental disorders, autism spectrum disorder or schizophrenia, comprising rilmenidine, a rilmenidine metabolite, or a pharmaceutically acceptable salt thereof.

Abstract: The present invention relates to a composition for preventing, improving, or treating fragile X syndrome or related developmental disorders, comprising lisuride, a lisuride metabolite, or a pharmaceutically acceptable salt thereof.

Abstract: The present invention relates to a pharmaceutical composition for preventing or treating autism spectrum disorder, which includes piperazine-1-carboxamidine or a pharmaceutically acceptable salt thereof as an active ingredient. In particular, the piperazine-1-carboxamidine of the present invention exhibits, in valproic acid-induced autism rat models, an effect of improving the degrees of social interaction and social preference, reducing repetitive or restricted behaviors, hyperactivity, and impulsive behaviors, and also enhancing electroshock-induced seizure threshold susceptibility, and thus the piperazine-1-carboxamidine of the present invention may be used as an active ingredient of a pharmaceutical composition for preventing or treating direct causative symptoms, such as hyperactivity, lack of sociability, and epileptic convulsions of autism spectrum disorder.