All members of a family do not have the same height, weight, and face. Here again, it's genetic and environmental differences that explain differences in our appearance and health. Some family members will inherit genes that predispose to autism, and others will not. Some family members will be exposed to environmental agents that trigger disease, and others will not. There is no autism in my family.
Any parents can have autistic children.
Because most children with autism do not grow up to have children of their own, almost all people with autism are born to parents who do not have the condition. There are presently no tests that can confirm or rule out the diagnosis. Further discoveries about DNA could lead to a gene test for autism. This would not only help parents and families, but would also accelerate the pace of research on autism. Identifying genes for autism would clarify the biological roots of the disease.