Causes and Prevalence

Causes:

The causes of Autism are not entirely understood. In fact, there are more than one set cause, much like there is more than just one form of Autism. There are many possible genetic factors and environmental factors that might play a role. "Over the last five years, scientists have identified a number of rare gene changes, or mutations, associated with autism. A small number of these are sufficient to cause autism by themselves" (Autism Speaks)

Outside of the body, many environmental factors may play a role "'[E]nvironmental,” stresses appear to further increase a child’s risk. The clearest evidence of these autism risk factors involves events before and during birth. They include advanced parental age at time of conception (both mom and dad), maternal illness during pregnancy and certain difficulties during birth, particularly those involving periods of oxygen deprivation to the baby’s brain" (Autism Speaks). Of the factors just mentioned, alone each factor would not cause Autism. It would take a combination of genetic and some of the environmental factors to cause Autism. 

Prevalence:

1in 88 American children are on the Autism Spectrum (Autism Society). This has increased ten-fold over the past 40 years. 

There does seem to be a gender bias. 1 in 54 boys are diagnosed to be on the spectrum. 1 in 252 girls are diagnosed to be on the spectrum (Autism Speaks).