According to the National Institute of Child Health and Human Development, current estimated cases of autism range from one in every 1,000 to one in every 500. Theories suggest vaccines are responsible, but there is growing concern that environmental toxins and pollution may be contributing factors. It is also theorized that nutrition, viral infections, immunizations and antibiotics may be causal aspects as well.
People speak in terms of children "developing" autism, but new research cited by the Autism Society of America suggest genetic ties -- that the disorder is present prenatal. An autism symptom will usually appear before the age of three, at which age a formal diagnosis can be made. Because an autism characteristic can be any combination of insufficiencies in language, social communication and cognition, autism is difficult to diagnose before normal development in these areas would usually occur.