According to US, autism genes are activated during fetal brain development. Autism-related mutations are connected to a pathway that regulates brain development.

This discovery was made when a set of well-known autism mutations called copy number variants or CNVs were being studied. These CNVs were later activated during a different stage in the development period of the brain. One that becomes active during the mid-fetal period were located in a region of the genome known as 16p11.2.