As of November 2015, research suggests that inherited and spontaneous genetic factors have a strong role in the development of autistic spectrum disorder, or autism, reports the National Institute of Neurological Disorders and Stroke. Autism seems to occur more frequently in children born of older parents and children born prematurely. Although scientists believe that environment also plays a role, they have not yet pinpointed specific factors.
Studies of families and twins indicate a link between inherited genetics and autism, explains the National Institute of Neurological Disorders and Stroke. In studies of identical twins, researchers discover that in 36 to 95 percent of cases, autism affects both twins rather than only one. Studies of families that already have one autistic child find that there is greater risk for autism in future children. Parents and relatives of children with autism sometimes display symptoms such as difficulties with communication, repetitive behavioral habits, schizophrenia or bipolar disorder.
Spontaneous gene mutations that occur in egg cells, sperm or during fertilization may also be responsible for autism, according to the National Institute of Neurological Disorders and Stroke. These mutations delete or duplicate single genes or whole strings of DNA and may account for cases of autism in families that show no predilection for the disorder.