yes, there are many mental illnesses associated with pku and high blood phe levels!! phenylalanine in your bloodstream builds up in your brain and prevents the formation of myelin, which is a conductor-like material that surrounds your neurons in the brain. no myelin means brain signals don’t travel as fast. hence the slower functioning and lower iq. anxiety, depression, and seizures can also be caused by too much phenylalanine in your blood. i dont know about other conditions for sure, but it would only make sense having too much of something in your brain could mess it up in a BUNCH of ways. :-S hope this helps!