[The problem L-Tryptophan was genetically engineered, see Jeffrey Smith video.]
The FDA Ban of L-Tryptophan: Politics, Profits and Prozac By: Dean Wolfe Manders, Ph.D.
Fazzolari-Nesci, A., Domianello, D., Sotera, V. and Raiha, N.C. (1992). Tryptophan fortification of adapted formula increases plasma tryptophan concentrations to levels not different from those found in breast-fed infants. J. Pediatric Gastroenterology and Nutrition. May. 14(4): 456-459.
The Health Dangers of Genetically Modified Foods
Infant formula feeding robs the developing brain of those essential biochemical nutrients, particularly the essential amino acids tryptophan and tyrosine, that are necessary for the normal development of the brain neurotransmitters serotonin and dopamine, which mediate the emotional behaviours of peace or violence, of happiness or depression and suicide. These are only two of the many brain neurotransmitters involved in the development of our emotional behaviours.  James W Prescott, Ph.D. Why breastfeeding mothers are important
It is also extremely doubtful, given the documented deficiencies of tryptophan in infant formula milk, that such a commercial preparation meets the magnitude of requirements of the other essential amino acids for infants that have been established by WHO. Table 2 lists the infant requirements for the essential amino acids compared to adult requirements (Merck Manual 1987). The damaging effects of such nutritional deficiencies in infant formula milk upon the developing brain, specifically brain neurotransmitters, have yet to be evaluated. The recent authorization by the FDA to provide the nutritional additives of two fatty acids, DHA (Docosahexaenoic Acid) and AA (Arachidonic Acid)-essential nutrients for brain development-to infant formula milk attests to the additional recognition that infant formula milk is malnutrition for normal brain development (Cunnane, et.at, 2000; Brody, 2001).  The Origins of Love & Violence: An Overview by James W. Prescott, Ph.D.