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Diseases Studied

The Rare Diseases Clinical Research Network is an NIH-funded research network of 20 active consortia or research groups working to advance treatment for diseases that are rare. Use the search tools on this page to find the diseases we currently study. You can reach out to the indicated consortia or research groups for more information on those diseases and studies underway.

This network focuses on clinical research and does not generally support clinical care outside of research activities. To learn about other rare diseases, please visit the Genetic and Rare Diseases Information Center (GARD), which is an NIH program that helps the public find reliable information about rare and genetic diseases. Their staff are specialists. Contact them at 1-888-205-2311 or email

All Diseases > Biopterin Synthesis or Recycling Defects

Biopterin Synthesis or Recycling Defects (BH4 Deficiency)

Disease Category: Phenylketonuria

Inherited (genetic) conditions that increase levels of the amino acid phenylalanine in the blood. They are part of a group of rare conditions known as tetrahydrobiopterin deficiencies. Babies with biopterin defect in cofactor biosynthesis cannot break down all of the phenylalanine from the proteins they eat. When left untreated, phenylalanine builds up to harmful levels in their body. Their body also makes fewer important chemicals for their brain called neurotransmitters. Symptoms include intellectual disability, seizures, depression, developmental delays, dystonia (involuntary muscle contractions), and parkinsonism.

Research groups studying this disease


Phenylalanine Families and Researchers Exploring Evidence (PHEFREE)

A collaboration of phenylketonuria (PKU) community members joining together as a national voice and supporting local efforts to raise PKU awareness and drive advocacy and education, while ultimately looking for a cure.