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Phenylketonuria (PKU)

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Introduction

Here you’ll find answers to some of the questions that parents often have about this condition. Additional resources are listed at the bottom of the page. Diagnosis and management information can be found in the PKU and Pterin Defects module, which is written for primary care clinicians but also may be of help to parents and family members. Information can also be found in the Newborn Screening page Phenylketonuria (PKU).

What is phenylketonuria (PKU) and what causes it?

Phenylketonuria (PKU) is a recessive disorder caused by deficiency in phenylalanine hydroxylase, the enzyme that converts the amino acid phenylalanine to tyrosine, leading to an accumulation of phenylalanine in the body. This accumulation is toxic for the development and functioning of the central nervous system and leads to intellectual disability. Phenylalanine is present in almost all foods containing proteins.

What are the symptoms of PKU?

With treatment and early introduction and maintenance of the special diet, normal IQ and development can be expected. Without treatment, symptoms in classic PKU begin by about 6 months of age. Initial symptoms may include:
  • a musty or "mousy" odor of the body and urine
  • developmental delays in sitting, crawling, and standing
  • microcephaly
If children remain untreated, they may develop:
  • decreased skin and hair pigmentation (due to lack of tyrosine)
  • eczema
  • seizures
  • profound intellectual disability

How it is diagnosed?

Most children with PKU are identified by newborn screening. If suspected after the newborn period, diagnosis is made by biochemical testing (a blood test). DNA testing can be used to confirm biochemical data.

What is the prognosis?

Prognosis is good for individuals with PKU who remain on the diet. Relaxation of diet is associated with executive function deficits and an increased risk of attention deficit disorder and problems in school.

What is the risk for other family members or future babies?

Inheritance is autosomal recessive. The only gene associated with PKU is phenylalanine hydroxylase (PAH) which is located on chromosome 12.

What treatments/therapies/medications are recommended or available?

Phenylalanine is present in almost all foods containing proteins and treatment of PKU involves a restrictive diet with reduction of phenylalanine and the addition of vitamins and minerals that are necessary for body metabolism. This requires special foods (medical formulas) that contain all amino acids except phenylalanine in addition to special low-protein foods.

How will my child and our family be impacted?

Although treatment with the diet is associated with an excellent prognosis, strict adherence to the diet can be difficult and expensive for families. Support from other families who are experiencing the same issues may be helpful - see information below for support groups. Your metabolic genetics clinic may also have resources that may be helpful.

Can I breastfeed my baby who has just been diagnosed with PKU?

It is often possible to breastfeed an infant with PKU, but this should be discussed in detail with the metabolic genetics team. Adjustments in your baby's diet may need to be made.

How expensive is Lofenalac and the other special supplements my child will need?

Insurance will usually provide formula and supplements for children with PKU if they are prescribed by your doctor.

Resources

Information & Support

Where can I go for further information?

For Parents and Patients

Support

Support for Rare Diseases (BioMarin)
Information with a special section for teens. Provides a clinic finder and a recipe section: BioMarin is a pharmaceutical company.

PKU Listserv
Share ideas and concerns with other PKU parents; login required.

General

Children's PKU Network
A non-profit organization that provides a free “newborn express pack” of information to help parents with newly a diagnosed child; provides links to food/formula suppliers, as well as links to many other related sites.

National PKU News
Includes information on diet, research, legislation, and support groups; provides a newsletter 3 times a year; and provides links to other resources and organizations.

Newborn Screening Disorder Information for Families
From the Utah Newborn Screening Program, this page lists 24 documents for families on different disorders that are screened including cystic fibrosis; biotinidase; galactosemia; organic acid disorders; amino acid disorders including PKU; fatty acid oxidation disorders; congenital adrenal hyperplasia; congenital hypothyroidism; sickle cell; sickle cell trait (carrier); Hb C; Hb D; Hb E; Hb C, D, or E trait (carrier); FABarts—alpha thalassemia syndrome; and unidentified hemoglobin trait (carrier).

Phenylketonuria (Genetics Home Reference)
Excellent, detailed review of condition for patients and families; sponsored by the U.S. National Library of Medicine.

PKU (MedlinePlus)
From the National Library of Medicine, a brief overview of PKU and links to other organizations with more information including nutrition information; a babysitter's guide; drugs containing phenylalanine; FAQs; tutorials; clinical trials; journal articles; support organizations; and more.

PKU - Information for Parents (STAR-G)
A fact sheet, written by a genetic counselor and reviewed by metabolic and genetic specialists, for families who have received an initial diagnosis of a newborn disorder; Screening, Technology and Research in Genetics.

Support for Rare Diseases (BioMarin)
Information with a special section for teens. Provides a clinic finder and a recipe section: BioMarin is a pharmaceutical company.

Patient Education

What is Phenylketonuria? (GSLC)
A brief educational overview of single gene disorders that includes the genetics of Phenylketonuria (PKU); Genetic Science Learning Center at the University of Utah.

Services in Montana

Select services for a different state: ID, NM, NV, RI, UT

Newborn Screening Programs

See all Newborn Screening Programs services providers (3) in our database.

Nutrition, Metabolic

See all Nutrition, Metabolic services providers (2) in our database.

Pediatric Genetics

See all Pediatric Genetics services providers (6) in our database.

Pediatric Metabolic Genetics

See all Pediatric Metabolic Genetics services providers (1) in our database.

For other services related to this condition, browse our Services categories or search our database.

Authors & Reviewers

Initial publication: October 2012; last update/revision: October 2015
Current Authors and Reviewers: