Blood phenylalanine concentrations are usually determined weekly during the first year of life, the period of maximal cerebral growth. Thereafter, blood tests can be done quarterly. Plasma amino acid concentrations are determined once or twice a year to be certain that tyrosine levels are adequate. Two additional points are important. A few phenylalanine-restricted food products are insufficiently fortified with vitamins and minerals.
If these products are used, blood selenium and vitamin B 12 levels should be checked annually. Multivitamin and mineral supplements are often prescribed for patients with PKU. The usual protein requirement to maintain growth in infants is about 2 to 3 g per kg per day. After growth patterns have stabilized, the requirement decreases gradually to 1 g per kg per day.
The adequacy of the diet is guided best by regularly determining blood phenylalanine and tyrosine levels, and assessing the infant's growth and development.
With a comprehensive approach, affected persons can be expected to develop normally. Already a member or subscriber? Log in. Interested in AAFP membership? Learn more. Koch is a graduate of the University of Rochester N. School of Medicine and completed a pediatric internship and residency at the Children's Hospital of Los Angeles, where he was chief resident in pediatrics.
Address correspondence to Richard K. Koch, M. Reprints are not available from the author. Influence of phenylalanine intake on phenylketonuria. Intellectual development in year-old children treated for phenylketonuria. Am J Dis Child. Koch JH. PKU: what's that? In: Koch J, ed. Robert Guthrie: the PKU story. Pasadena, Calif. Koch R, Wenz E. Annu Rev Nutr. Maternal phenylketonuria and hyperphenylalaninemia. An international survey of the outcome of untreated and treated pregnancies.
N Engl J Med. In: Scriver CR, ed. The metabolic and molecular bases of inherited disease. New York, N. Guthrie R. Blood screening for phenylketonuria. PKU is a genetic disorder that prevents the normal breakdown of a protein found in some foods.
Proteins are made up of building blocks called amino acids; in PKU, the body cannot break down the amino acid phenylalanine. Because phenylalanine cannot be broken down metabolised normally, it builds up in the blood and tissues. This build-up prevents the brain from developing properly. Progressive intellectual disability results if PKU is not treated from early infancy.
With treatment, children with PKU can grow and develop normally. All newborn babies are tested for PKU through the newborn screening test taken during the first few days of life.
About one in 10, newborn babies are affected with PKU. See our video on newborn bloodspot screening and PKU. Genes are inherited particles found in all cells of our body.
They form the blueprints for all growth, development and functions of the body. Each gene is responsible for sending a message that tells the cells how to make a particular product. The PKU gene tells the cell to make an enzyme that breaks down the amino acid phenylalanine.
Even though most babies with PKU are diagnosed soon after birth, screening for PKU should be considered for any child who has an intellectual disability or is developmentally delayed. Some babies adopted from other countries may also need to be screened for PKU and other inherited illnesses in the first year of life. Newborns are also tested for other metabolic birth defects often before they leave the hospital.
Test results may vary depending on your child's age, gender, health history, the method used for the test, and other things. Your child's test results may not mean they have a problem.
Ask the healthcare provider what the test results mean for your child. The test screens for blood levels of phenylalanine. The test will be first done after your baby is 24 hours old, then may be repeated when your baby is 7 to 14 days old. Babies are often screened for PKU with a heel-prick test. This is done by getting a few drops of blood from the infant's heel.
A urine test is an alternative to the heel prick. The healthcare provider will collect a sample of your baby's urine. Having a heel-prick test carries some risks. Top of the page.
Test Overview A phenylketonuria PKU test is done to check whether a newborn baby has the enzyme needed to use phenylalanine in their body. Why It Is Done A phenylketonuria PKU screening test is done to see whether a newborn baby has the enzyme needed to use phenylalanine in their body. How To Prepare You do not need to do anything before your baby has this test.
How It Is Done A heel stick is used to get a blood sample from a baby. How It Feels A brief pain, like a sting or a pinch, is usually felt when the lancet punctures the skin. Risks There is very little risk of a problem from a heel stick. Results If the heel stick screening test shows high phenylalanine levels, a blood sample is taken from your baby's vein.
References Citations U. Preventive Services Task Force Screening for phenylketonuria PKU.
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