DHPR Deficiency (Biopterin Deficiency) Dihydropteridine reductase (DHPR) deficiency is a disorder of tetrahydrobiopterin metabolism. Tetrahydrobipterin plays a role as a cofactor in Phenylalanine, L-Dopa and Serotonin metabolism. Thus deficiencies are mostly associated with hyperphenylalaninemia, and deficiency of Dopamine and Serotonine. Unless diagnosed by newborn screening via high blood phenylalanine levels, patients develop neurological problems within the first year of life, including progressive developmental delay, seizures, microcephaly, and parkinsonian dystonia. Episodes of irritability, lethargy, poor temperature control and other vegetative dysfunctions are common in severe cases. Significant cerebral atrophy and calcifications have been particularly described in DHPR deficiency. DHPR deficiency should be suspected in all infants with a positive neonatal screening test for phenylketonuria, especially when hyperphenylalaninemia is moderate.