Autism is a physical disorder linked to abnormal biology and chemistry in the brain. The exact causes of these abnormalities remain unknown, but this is a very active area of research. Genetic factors seem to be important. For example, identical twins are much more likely than fraternal twins or siblings to both have autism. Similarly, language abnormalities are more common in relatives of autistic children. Chromosomal abnormalities and other neurological problems are also more common in families with autism.
Researchers supported by NIMH and other National Institute of Health (NIH) institutes are studying how an autistic brain differs from a normal brain. Some researchers are investigating potential defects that occur during initial brain development; others are looking for defects in the brains of people already diagnosed with autism.
Recent neuroimaging studies have shown that a contributing cause for autism may be abnormal brain development beginning in the infant's first months. This "growth dysregulation" theory holds that the anatomical abnormalities seen in autism are caused by genetic defects in brain-growth factors. It is possible that sudden, rapid head growth in an infant may be an early warning signal that will lead to early diagnosis and effective biological intervention or possible prevention of autism.
