The Autism Spectrum is a diverse group of neurodevelopmental disorders that share a common set of characteristics, which includes restricted interests, repetitive behaviors and difficulties with social interaction and communication. The biggest known risk factors for autism are genes. However, the mutations that have been firmly implicated in autism are unlike the genetic variants that explain common late-onset diseases such as heart disease and diabetes. Most of the genes or genomic regions that are known to contribute to autism are “mutation hotspots”. Disease-causing variants confer significant risk. Such variants segregate in families over a few generations or can be observed as spontaneous mutations (DNMs) in an affected child. From the perspective of genetics, the characteristic of humans that is most clearly reflected in autism is the intrinsic mutability of our genome.