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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 > GTP cyclohydrolase 1 deficiency (recessive form)

GTP cyclohydrolase 1 deficiency (recessive form) (GTPCH1 deficiency)

Disease Category: Phenylketonuria

A genetic disorder causing high blood levels of the amino acid phenylalanine. This condition also causes abnormally low levels of neurotransmitters, which transmit signals between nerve cells in the brain. When not treated, symptoms include abnormalities of muscle tone, delays in motor development, convulsions, drowsiness, irritability, abnormal movements, hyperthermia, hypersalivation, and difficulty swallowing.

Research groups studying this disease


Phenylalanine Families and Researchers Exploring Evidence (PHEFREE)