dihydropteridine reductase deficiency
Dihydropteridine reductase (DHPR) deficiency is a severe form of hyperphenylalaninemia (HPA) due to impaired regeneration of tetrahydrobiopterin (BH4), leading to decreased levels of neurotransmitters (dopamine, serotonin) and folate in cerebrospinal fluid, and causing neurological symptoms such as psychomotor delay, hypotonia, seizures, abnormal movements, hypersalivation, and swallowing difficulties.