PTS and hyperinsulinemic hypoglycemia, familial, 4: Among the 99 patients, 93 (93.9%) had hyperphenylalaninemia-phenylketonuria, 2 (2.0%) had tetrahydrobiopterin metabolism disorders [one due to 6-pyruvoyl-tetrahydropterin synthase (PTPS) deficiency and the other due to dihydropteridine reductase (DHPR) deficiency], 3 (3.0%) had maternal PKU syndrome (one of whom also had mild phenylketonuria), and 1 (1.0%) had transient hyperphenylalaninemia.