ASDs are thought to be caused by a combination of genes, biochemical, and environmental variables. Researchers are looking into several genes that are thought to play a role in the development of these disorders, as well as several brain areas that have been related to them. Structure irregularities in the mirror neuron networks, for example, are being investigated in the first months of life to see if hereditary and/or external conditions are to blame.  The consequences of genetic imprinting, in which the activation of a gene is controlled by which parent contributes the gene copy, are also being investigated. Dopamine, epinephrine, and serotonin are just a few of the neurotransmitters that might malfunction. In other cases, scientists are investigating the possibility that the disease is caused by a defective immunological response to a virus, high protein levels in the bloodstream at birth, disruption of specific neuropeptides, or significant stress during pregnancy.