[ellisv]

It's important to note our understanding is far from complete. There may be more genes associated with autism than we currently know. So 30% of cases may have a known genetic factor but that doesn't mean 70% don't have a genetic component.

[azinman2]

True. But we’ve also seen environmental correlations as well, as well as things like age of the father, etc.

[ellisv]

This is also explained as a genetic factor as chromosomal abnormalities and replication errors are more frequent although cumulative environmental exposures may also play a role.