ABSTRACT
INTRODUCTION Although some people may still believe in the psychogenic hypothesis of autistic disorder (autism), most authorities in the field of autism agree that neurobiological factors are of crucial importance in terms of causes of autism. An important piece of evidence that supports the neurobiological hypothesis is the association of mental retardation with autism: About three out of four individuals with autism also have lower cognitive functioning (i.e., mental retardation), which generally indicates some serious damage or dysfunction of the brain. In addition to the presence of global mental retardation, certain neurological abnormalities have been reported in 30% to 75% of several groups of individuals with autism (reviewed by Tsai, 1999). Furthermore, the majority of the individuals with autism have severe impairment in speech and language development which reflects damage or dysfunction of certain brain structure or of the neurological system. However, despite strong evidence pointing to a neurobiological etiology of autism, the exact cause (s) and nature of the basic defect remain unclear.
