[sjg007]

ADHD is certainly not Mendelian. There are likely multiple genes involved probably around specific pathways.

https://www.nature.com/articles/s41380-018-0070-0

[lazide]

Seems like it’s about 75% heritable (if one or both parents have it), definitely not clearly recessive.

[astrange]

"Heritable" doesn't mean it's genetic. You exist in the same environment as your parents - literally you're born inside them.

[sjg007]

There's epigenetics. This is why we see differences with monozygotic twins.

[astrange]

That's if you started studying them right after birth maybe, but otherwise it's more likely one had more childhood lead exposure than the other or ate different diets, things like that.

Air pollution in particular seems to be really really bad for all kinds of health.