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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 > Phenylalanine hydroxylase deficiency

Phenylalanine hydroxylase deficiency (PAH Deficiency)

Alternative Names: Phenylketonuria (PKU)

Disease Category: Phenylketonuria

An inherited disorder characterized by low levels or absence of the enzyme phenylalanine hydroxylase (PAH). When PAH is absent or deficient, the amino acid phenylalanine accumulates within the body, becoming toxic to the brain. When not treated, symptoms include mild to severe intellectual disability, depression, parkinsonism, seizures, and developmental delays.

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.