Dihydropteridine Reductase Deficiency

Dihydropteridine reductase deficiency (DHPR) is a severe form of hyperphenylalaninemia (high levels of the amino acid phenylalanine in the blood) due to impaired renewal of a substance known as tetrahydrobiopterin (BH4). Tetrahydrobiopterin normally helps process several amino acids, including phenylalanine, and it is also involved in the production of neurotransmitters. If little or no tetrahydrobiopterin is available to help process phenylalanine, this amino acid can build up in the blood and other tissues and the levels of neurotransmitters (dopamine, serotonin) and folate in cerebrospinal fluid are also decreased. This results in neurological symptoms such as psychomotor delay, low muscle tone (hypotonia), seizures, abnormal movements, too much salivation, and swallowing difficulties. DHPR deficiency is caused by mutations in the QDPR gene. It is inherited in an autosomal recessive manner. Treatment should be started as soon as possible and includes BH4 supplementation usually combined with a diet without phenylalanine, folate supplementation, and specific medications to restore the levels of neurotransmitters in the brain.