I'm a clinical psychologist, and the information you're providing is just not true. There are a ton of peer-reviewed studies that show there is a higher chance of being diagnosed with ADHD when there is child abuse, marital conflict or smoking during the pregnancy (example). These factors are environmental.
It is impossible to know "the cause" of ADHD, because ADHD is not a disease. It's just the name we give to all the people whose behavior meets the diagnostic criteria. Those percentages are just his personal speculation.
The scientific community THINKS there is a link with neurotransmitters and the prefrontal cortex, but we just don't know enough about how the brain works to actually prove this.
Yes, the gene by environment interaction. Your environment can "activate" certain genes that wouldn't necessarily be activated without that environment. An example I like is, let's say John has a family history of severe substance use disorders. John is at higher risk of developing a substance use disorder because of his family history but he decides he's never going to drink or use drugs. John doesn't develop a substance use disorder because he's never in that environment. He likely has the genetic influences but not the environment. With psychological disorders, it usually takes both the genetic heritability and the environment.
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u/HD_ERR0R May 30 '17 edited May 30 '17
Based on Dr. Russell environment alone can't cause ADHD. But can play a factor in making symptoms worse or triggering 1 or more of 5 genes.
10 min causation of ADHD part 1
4min causation of ADHD part 2
4min causation of ADHD part 3
Full lecture
same video broken up into parts to be more ADHD friendly
Edit: reworded.
This part of ADHD is still not fully known yet.