Twin studies in autism: what might they say about genetic and environmental influences.

Baum (2012) wrote a think-piece, not an experiment.

The author asked: if one identical twin has autism and the other does not, where does the gap come from?

Most twin studies blame "the environment." M says wait—chemical tags on DNA can drift even when genes stay the same.

The paper finds no new data. Instead it warns that epigenetic drift can make identical twins look like they grew up in different worlds.

If we ignore these tiny chemical changes, twin studies may over-count environmental causes and under-count biology.

Weiss et al. (2021) later measured actual methylation in severely affected kids. They found clear sex-specific patterns, proving the drift M warned about is real and measurable.

Melnyk et al. (2012) showed autistic children already carry less methylation and more oxidative stress than their siblings. Their numbers give a body-based reason for the gaps M described.

Bowen et al. (2012) hunted rare mutations in methylation-control genes. Their gene-first angle and M’s tag-first angle meet in the same pathway: both say "check the switches, not just the sequence."

When you read that "autism is 90 % genetic because twins match," pause. Epigenetic drift means even identical pairs can diverge before birth. For your assessments, this keeps the door open for biomedical and behavioral tweaks that target gene switching rather than the genes themselves. It also reminds us to treat each twin as a unique client, not a genetic copy.