Nental retrardation. All infants in the U.S. Are tested for this at birth. The only way to prevent menat retardation is by special diet.
Blond/slow/seizures. For babies born without newborn screening this is a significant risk. They have blonder hair than they should (metabolic thing), develop slowly and eventually have seizures and diminished intellect. State screening programs have been screening for this since the 1960's, and rarely miss a case.