Autism spectrum disorders are characterized behaviorally by expressive language and social deficits, the performance of stereotypic and repetitive behavior patterns, and abnormal cognitive functioning. Children with autism spectrum disorders often do not have known anomalies seen on genetic testing. An emerging paradigm suggests that the majority of children with autism are displaying a pattern of genetic / environmental interaction that make them susceptible to difficulties with detoxification of the heavy metal and chemical environment. Children with autism demonstrate increased difficulty with the performance of methylation and sulfation required for the elimination of fat soluble chemicals from human tissues. These children also commonly display dysfunction of their metalloprotein systems necessary for the elimination of heavy metals such as mercury and arsenic from their bodies.