It is thought that some mixture of genetic, biological, and environmental variables causes ASDs. Researchers are investigating several genes that are thought to contribute to the growth of these diseases as well as several brain areas associated with the diseases.
Abnormal brain development is being researched during the first months of life to determine if genetic and/or environmental variables can cause structural defects, such as in the mirror neuron systems. Researchers also investigate the impacts of genetic imprinting in which the expression of a gene is determined by the parent giving the gene copy. In some instances, researchers explore the chance that a defective immune response to a virus, high blood protein levels at birth, dysregulation of neuropeptides, or significant stress during pregnancy or deficiency of oxygen at the time of birth may lead to the disease.