Phenylketonuria (fen-ul-keetone-YU-ree-ah, or PKU) is an inherited metabolic disorder in which the body cannot completely break down the protein (amino acid) phenylalanine. This happens because a necessary enzyme, phenylalanine hydroxylase, is deficient. Because of this, phenylalanine builds up in the body’s cells and causes nervous system damage.
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(Screening for PKU in premature babies is different and more difficult for several reasons.)
Each year 10,000 to 15,000 babies are born with the disease in the United States and Phenylketonuria occurs in both males and females of all ethnic backgrounds (although it is more common in individuals of Northern European and Native American heritage.)
Symptoms
PKU disease symptoms may include:
Diagnosis
The test is highly accurate if done when the infant is more than 24 hours old but less than seven days old. If an infant is tested at less than 24 hours old, it is recommended that the test be repeated when the infant is one week old. As noted above, premature babies need to be tested in a different manner for several reasons including a delay in feedings.
Treatment
Because phenylketonuria is a problem of breaking down phenylalanine, the infant is given a special diet that is extremely low in phenylalanine.
At first, a special low-phenylalanine infant formula (Lofenalac) is used.
Individuals must remain on a phenylalanine-restricted diet during childhood and adolescence.
Some individuals are able to reduce their diet restrictions as they grow older. Regular blood tests are needed to measure the levels of phenylalanine, and the diet may need to be adjusted if the levels are too high. In addition toa restricted PKU disease diet, some individuals may take the drug Kuvan (sapropterin) to help lower phenylalanine levels in the blood.
A Complete Guide to a Low-Protein Diet
Monitoring
As noted, blood tests are used to monitor people with PKU. At the present time guidelines recommend that the target blood concentration of phenylalanine should be between 120 and 360 uM for people with PKU of all ages. Sometimes a limit as high as 600 uM is allowed for older adults. Pregnant women, however, are required to follow their diet more strictly, and a maximum level of 240 uM is recommended.
Studies looking at compliance (the number of people who follow their diet and meet these guidelines) is at 88 percent for children between birth and age four, but only 33 percent in those who are age 30 and over.
Managing PKU in Adolescence and AdulthoodWhile healthcare providers emphasize the need to control phenylalanine levels until age 12 to support cognitive development, research shows that limiting dietary intake of phenylalanine may be important throughout life. Phenylalanine levels may continue to affect the brain during the teen and adult years. In fact, higher than recommended phenylalanine levels in these years may result in a lower IQ.Continuing a restricted diet into adulthood can cause a lower quality of life for some people, but the overall cognitive benefits may offset the negative aspects.
Managing PKU in Adolescence and Adulthood
While healthcare providers emphasize the need to control phenylalanine levels until age 12 to support cognitive development, research shows that limiting dietary intake of phenylalanine may be important throughout life. Phenylalanine levels may continue to affect the brain during the teen and adult years. In fact, higher than recommended phenylalanine levels in these years may result in a lower IQ.Continuing a restricted diet into adulthood can cause a lower quality of life for some people, but the overall cognitive benefits may offset the negative aspects.
While healthcare providers emphasize the need to control phenylalanine levels until age 12 to support cognitive development, research shows that limiting dietary intake of phenylalanine may be important throughout life. Phenylalanine levels may continue to affect the brain during the teen and adult years. In fact, higher than recommended phenylalanine levels in these years may result in a lower IQ.
Continuing a restricted diet into adulthood can cause a lower quality of life for some people, but the overall cognitive benefits may offset the negative aspects.
Role of Genetics
PKU in Pregnancy
Young women with phenylketonuria who do not eat a phenylalanine-restricted diet will have high levels of phenylalanine when they become pregnant. This can lead to serious medical problems known as PKU syndrome for the child, including mental retardation, low birth weight, heart birth defects, or other birth defects. However, if the young woman resumes a low-phenylalanine diet at least 3 months prior to pregnancy, and continues on the diet throughout her pregnancy, PKU syndrome can be prevented. In other words, a healthy pregnancy is possible for women with PKU as long as they plan ahead and carefully monitor their diet throughout pregnancy.
Research
Coping
Coping with PKU is difficult and requires great commitment since it is a life-long endeavor. Support can be helpful and there are many support groups and support communities available in which people can interact with others coping with PKU both for emotional support and to stay up-to-date on the latest research.
There are several organizations, as well, which work to support people with PKU and fund research into better PKU disease treatments. Some of these includeThe National Society for Phenylketonuria, theNational PKU Alliance(part of the organization NORD, the National Organization for Rare Disorders, andThe PKU Foundation. In addition to funding research, these organizations provide help which can range from providing assistance for the purchase of the special formula required for infants with PKU to providing information to help people learn about and navigate their way to an understanding of PKU and what it means in their lives.
Frequently Asked Questions
No. Phenylketonuria is a lifelong condition. However, complications such as intellectual disabilities can be prevented with a proper diet.
Learn MoreGuide to Breastfeeding
Yes. If both parents are carriers of the PAH gene with a mutation, their child has a 25% chance of being born with PKU.Learn MoreWhat Is Genetic Predisposition?
Yes. If both parents are carriers of the PAH gene with a mutation, their child has a 25% chance of being born with PKU.
Learn MoreWhat Is Genetic Predisposition?
4 SourcesVerywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Cazzorla C, Bensi G, Biasucci G, et al.Living with phenylketonuria in adulthood: The PKU ATTITUDE study.Molecular Genetics and Metabolism Reports.2018;16:39-45. doi:10.1016%2Fj.ymgmr.2018.06.007National Institute of Health.What are common treatments for phenylketonuria (PKU)?Banta-Wright SA, Press N, Knafl KA, Steiner RD, Houck GM.Breastfeeding infants with phenylketonuria in the united states and canada.Breastfeeding Medicine. 2014;9(3):142-148. doi:10.1089%2Fbfm.2013.0092National Human Genome Research Institute.About Phenylketonuria.Additional ReadingJurecki, E., Cederbaum, S., Kopesky, J. et al.Adherence to Clinic Recommendations Among Patients with Phenylketonuria in the United States.Molecular Genetics and Metabolism. 2017. (Epub ahead of print).Van Spronsen, F., van Wegberg, A., Ahring, K. et al.Key European Guidelines for the Diagnosis and Management of Patients with Phenylketonuria.Lancet Diabetes and Endocrinology. 2017. (Epub ahead of print).Vockley, J., Andersson, J., Antshel, K. et al.Phenylalanine Hydroxylase Deficiency: Diagnosis and Management Guideline.Genetics in Medicine. 2014;16(2):188-200.
4 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Cazzorla C, Bensi G, Biasucci G, et al.Living with phenylketonuria in adulthood: The PKU ATTITUDE study.Molecular Genetics and Metabolism Reports.2018;16:39-45. doi:10.1016%2Fj.ymgmr.2018.06.007National Institute of Health.What are common treatments for phenylketonuria (PKU)?Banta-Wright SA, Press N, Knafl KA, Steiner RD, Houck GM.Breastfeeding infants with phenylketonuria in the united states and canada.Breastfeeding Medicine. 2014;9(3):142-148. doi:10.1089%2Fbfm.2013.0092National Human Genome Research Institute.About Phenylketonuria.Additional ReadingJurecki, E., Cederbaum, S., Kopesky, J. et al.Adherence to Clinic Recommendations Among Patients with Phenylketonuria in the United States.Molecular Genetics and Metabolism. 2017. (Epub ahead of print).Van Spronsen, F., van Wegberg, A., Ahring, K. et al.Key European Guidelines for the Diagnosis and Management of Patients with Phenylketonuria.Lancet Diabetes and Endocrinology. 2017. (Epub ahead of print).Vockley, J., Andersson, J., Antshel, K. et al.Phenylalanine Hydroxylase Deficiency: Diagnosis and Management Guideline.Genetics in Medicine. 2014;16(2):188-200.
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
Cazzorla C, Bensi G, Biasucci G, et al.Living with phenylketonuria in adulthood: The PKU ATTITUDE study.Molecular Genetics and Metabolism Reports.2018;16:39-45. doi:10.1016%2Fj.ymgmr.2018.06.007National Institute of Health.What are common treatments for phenylketonuria (PKU)?Banta-Wright SA, Press N, Knafl KA, Steiner RD, Houck GM.Breastfeeding infants with phenylketonuria in the united states and canada.Breastfeeding Medicine. 2014;9(3):142-148. doi:10.1089%2Fbfm.2013.0092National Human Genome Research Institute.About Phenylketonuria.
Cazzorla C, Bensi G, Biasucci G, et al.Living with phenylketonuria in adulthood: The PKU ATTITUDE study.Molecular Genetics and Metabolism Reports.2018;16:39-45. doi:10.1016%2Fj.ymgmr.2018.06.007
National Institute of Health.What are common treatments for phenylketonuria (PKU)?
Banta-Wright SA, Press N, Knafl KA, Steiner RD, Houck GM.Breastfeeding infants with phenylketonuria in the united states and canada.Breastfeeding Medicine. 2014;9(3):142-148. doi:10.1089%2Fbfm.2013.0092
National Human Genome Research Institute.About Phenylketonuria.
Jurecki, E., Cederbaum, S., Kopesky, J. et al.Adherence to Clinic Recommendations Among Patients with Phenylketonuria in the United States.Molecular Genetics and Metabolism. 2017. (Epub ahead of print).Van Spronsen, F., van Wegberg, A., Ahring, K. et al.Key European Guidelines for the Diagnosis and Management of Patients with Phenylketonuria.Lancet Diabetes and Endocrinology. 2017. (Epub ahead of print).Vockley, J., Andersson, J., Antshel, K. et al.Phenylalanine Hydroxylase Deficiency: Diagnosis and Management Guideline.Genetics in Medicine. 2014;16(2):188-200.
Jurecki, E., Cederbaum, S., Kopesky, J. et al.Adherence to Clinic Recommendations Among Patients with Phenylketonuria in the United States.Molecular Genetics and Metabolism. 2017. (Epub ahead of print).
Van Spronsen, F., van Wegberg, A., Ahring, K. et al.Key European Guidelines for the Diagnosis and Management of Patients with Phenylketonuria.Lancet Diabetes and Endocrinology. 2017. (Epub ahead of print).
Vockley, J., Andersson, J., Antshel, K. et al.Phenylalanine Hydroxylase Deficiency: Diagnosis and Management Guideline.Genetics in Medicine. 2014;16(2):188-200.
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