QDPR and hyperinsulinemic hypoglycemia, familial, 4: In this group, 2 patients (33%) were identified by positive newborn screening for PKU: one had PTPS deficiency and another one had DHPR deficiency in the neonatal period based on the response to sapropterin loading test, or non-detectable DHPR enzyme activity on dried blood spots or elevated urine neopterin and neopterin to biopterin ratio.