Running Header: Phenylketonuria
University of Minnesota, School of Nursing
Phenylketonuria (PKU) is a genetic inborn error of metabolism. This means that one of the functions of metabolism in the body is not functioning properly due to a genetically transmitted gene. The body requires eight essential amino acids for growth and development that must be obtained from the diet, phenylalanine is one of these eight. Approximately half of the phenylalanine that is taken into the body is used for protein production and the other half is converted into tyrosine (Bowe, 1995). The malfunctioning of PKU is that the enzyme, phenylalanine hydroxylase (dictionary, 1999), used for conversion of phenylalanine to tyrosine is either deficient or non-existent in the body. This leads to the accumulation of phenylalanine in the blood, incomplete degredation of phenylalanine resulting in accumulation of its metabolites and decreased tyrosine (Bowe, 1995). This minor metabolic malfunction in the body can cause great discepencies between the PKU and non-PKU patient.
Phenylalanine excess and tyrosine deficiencies result in many physiologic alterations in the PKU patient. The main problem is that excess phehylalanine in the blood inhibits normal brain development. This results in mental retardation, short attention span, poor short term memory, problems with visual motor perception and motor coordination seizures and behavior problems of the untreated patient (Bowe, 1995) (Text, 0000). Excess phenylalanine metabolites also show up in the urine and perspiration giving the patient a musty odor and skin conditions such as eczema and seborrhea. Tyrosine deficiencies cause PKU patients to have decreased epinephrine levels and reduced melanin production resulting in very fair skin, and light colored eyes and hair. Phenylalanine and tyrosine levels must be controlled in order to successfully treat the patient.(Bowe, 1995)
Phenylalanine levels must be controlled soon after birth in order to allow for proper growth and development and brain function. Early screening for PKU is a necessity, so that amino acid levels can be properly controlled through treatment. The screening must take place at least 2 days after the first milk feeding because phenylalanine must be given time to build up from the child's nutient intake, however it must be initiated soon enough for treatment to start within 3 weeks. It is recommended that the child get the screen before leaving the hospital. The screening requires testing a small amount of the babies blood (Bowe, 1995).
Despite the devastating effects of PKU, with early identification and detailed nutritional monitoring the PKU patient can overcome most of the devastating effects of the disease. Treatment is aimed at providing enough phenylalanine nutritionally for growth and development without excessive accumulation of it (Lott, 1988). PKU patients need to maintain a serum phenylalanine level of between 2.0 and 8.0 mg/dl (Bowe, 1995). While the child is young a low-phenylalanine formula is given to baby that supplies it's total nutrition. Once the child begins to eat solid foods the diet becomes more complex. They must eat almost no natural protein foods and limited other foods. They are allowed to eat fruits and juices and some vegetables and a large majority of their diet may still be a special formula, which can be flavored specially. Phenylalanine free foods are also sold like pastas and flour. Special low phenylalanine diets are recommended for life and have been shown to rarely cause problems of there own (due to low phenylalanine). (Bowe, 1995)
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Bowe, K. (1995). Phenylketonuria: an update for pediatric community health nurses. Pediatric Nursing, 21 (2), 191-194
Lott, J.W. (1988). PKU: a nursing update. Journal of Pediatric Nursing, 3 (1), 29-33.
Scriver, C. R., Beaudet, A. L., Sly, W. S. & Valley, D. (1995) The Metabolic and Molecular Bases of Inherited Disease. (1), (7th ed.) New York: Mosby.