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Phenylketonuria (PKU): Overview

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Phenylketonuria (pronounced fen-l-kee-toh-NOOR-ee-uh), often called PKU, is caused by phenylalanine hydroxylase (PAH) deficiency. It is an inherited disorder that that can cause intellectual and developmental disabilities (IDDs) if not treated. In PKU, the body can't process a portion of a protein called phenylalanine (pronounced fen-l-AL-uh-neen), which is in all foods containing protein. High levels of phenylalanine can cause brain damage. PAH deficiency produces a spectrum of disorders, including PKU, non-PKU hyperphenylalaninemia, and variant PKU. Classic PKU is caused by a complete or near-complete deficiency of PAH.

All children born in U.S. hospitals are screened routinely for PKU soon after birth, making it easier to diagnose and treat affected children early. And pregnant women may request prenatal testing to determine if their fetus is at risk for PKU.

The NICHD, other branches of the NIH, and various scientific organizations continue working to better understand, diagnose, and treat PKU. Since NICHD was established, it has played a key role in PKU-related research, with its support of studies on the safety and effectiveness of a restricted diet to treat PKU and to prevent PKU-related IDD. In recent years, NICHD-supported research areas included maternal PKU, long-term management of the disorder, and possible new treatments such as gene therapy.

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Common Name

  • PKU

Medical or Scientific Names

  • Phenylketonuria
  • Folling's Disease
  • PAH deficiency
  • Phenylalanine Hydroxylase (pronounced hahy-DROK-suh-leys) Deficiency Disease
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