Since we do not make enough BH4 (tetrahydrobiopterin) with this enzyme deficiency we cannot metabolize the amino acids needed to make serotonin, dopamine, and Nirtic Oxide. And then some of these amino acids turn into trace amines that act like meth.
The deficiency causes problems with amino acid metabolism, which themselves mess up the brain.
The depression was a mere symptom of the underlying disease. When you read the DSM, you realize there are no mental illnesses, just syndromes: sets of signs and symptoms. Except in select few cases, the pathophysiology is unknown.
Protein is split into amino acids and then recombined into proteins inside body. The splitting process and recombination process need glucose in blood and, effectively, drain glucose from blood.
In my experience, some of the amino acid sport drinks can drain glucose from blood to the point where I had clear signs of very low glucose levels, including restlessness and shaking limbs.
The glucose level may affect mood and has other interesting effects.
If you look at what carbs, fats and proteins do with you mood, I think you will see that carbs make one relaxed (see relation between carbs and orexin), fats make one jolly (due to endocannabioids) and proteins make one awake (draining carbs from blood, mainly).
