Phenylketonuria (PKU)


The Questions and Answers that follow aim to provide an introduction to phenylketonuria (PKU) for parents and other family members. Following those, we offer links to selected resources for more information and support and a list of valuable services.
More information about many topics relevant to children with PKU and many other chronic conditions and their families can be found in the left menu. Detailed information aimed at primary care doctors can be found in our PKU and Pterin Defects module. 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.


Information & Support

Where can I go for further information?

For Parents and Patients


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.


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
Information for families about newborn screening disorders; Utah Department of Health, Newborn Screening Program.

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.

Genetics in Primary Care Institute (AAP)
Contains health supervision guidelines and other useful resources for the care of children with genetic disorders; American Academy of Pediatrics.

National Urea Cycle Disorders Foundation
Support and information that includes medical lectures on urea cycle disorders, nutrition and medication resources, and information about events and conferences.

Services for Patients & Families in Utah (UT)

For services not listed above, browse our Services categories or search our database.

* number of provider listings may vary by how states categorize services, whether providers are listed by organization or individual, how services are organized in the state, and other factors; Nationwide (NW) providers are generally limited to web-based services, provider locator services, and organizations that serve children from across the nation.

Authors & Reviewers

Initial publication: October 2012; last update/revision: October 2015
Current Authors and Reviewers:
Author: Lynne M. Kerr, MD, PhD