The methylation, neurotransmitter, and antioxidant connections between folate and depression. Read Study 

Dr Bill Walsh 
The Walsh Institute http://www.walshinstitute.org
http://www.biobalance.org.au

Pfieiffer Institute http://www.hriptc.org/index.php
There are many others who have been doing nutritional research into the causes and natural treatment of mental illness, which is affecting untold billions around the world. Dr. Fredericks, Dr. Linus Pauling,, Dr. Bernard Rimland, Dr. H.I. Newbold, Dr. William Philpott, Dr. Marshall Mandell, Dr. Abram Hoffer, Dr. Humphrey Osmond, Dr. Carl Pfeiffer, Dr. Alan Cott, Dr. David Hawkins, Dr. Paul Dunn, Dr. Ray Wunderlich 


Information on some of the genes (and polymorphisms) associated with ADHD
http://www.failsafediet.com/the-genetics-of-adhd/