Phenylketonuria, or PKU, is an inherited disorder in the metabolism of protein, causing a person to have difficulty breaking down the specific amino acid, phenylalanine, or phe. If this disorder is left unidentified and untreated, the Phe will accumulate in the body and over time will become toxic to the brain, resulting in mental retardation and other neurological problems. The good news is that the mental retardation outcome is one of the past. In the mid-1960s the United States implemented a newborn screening program to identify and treat these children early on to prevent any neurological damage.
Diagnosis
The newborn screen for PKU is a tool to identify a possible disorder. Once a positive newborn screen result for PKU is found, the baby will need to have additional testing for confirmation of the disorder as soon as possible. A metabolic center will be contacted to assist with making the diagnosis of PKU. Once the disorder has been confirmed, it is essential to start the low phenylalanine diet under the guidance by a metabolic physician and registered dietitian. Ideally, the diet is started within seven to 10 days of birth.
Diet Intervention
The diet intervention for treatment of PKU consists of two parts, a special metabolic formula, free of phe, and a low phe diet. The metabolic formula is an essential dietary component for all ages with PKU to support optimal growth and development. The metabolic formula provides ample phe free protein, vitamins, minerals and extra tyrosine, an amino acid that becomes essential for people with PKU. The low phe diet may be a little more challenging. High amounts of phe are found in all foods of animal origin, including meat, poultry, fish, dairy, eggs, as well as beans, nuts, bread, pastas, cereals, and foods made with aspartame. A few food manufacturers make specialty low phenylalanine foods to substitute for these naturally high protein foods. Fruits and vegetables are lower in phe, and therefore are staples in the PKU diet.
Diet Management
PKU is a lifelong condition; it is present in the person from birth and will always be a part of his life, as there is not a cure. In the past, it was thought safe to discontinue the diet at ages 4, 6, or 12 years of age, but after studying the long term decline in intellect and performance, clinicians are in agreement that the PKU diet should be followed for life for the best outcome. There are some promising new therapies that may allow for a less restrictive diet, but not a discontinuation of the diet.
Monitoring
Blood tests measuring phenylalanine in the body are the key to diet management and support the best outcomes for the person with PKU. The desired phe levels for all ages are between 120 and 360 umol/L, or (2 to 6 mg/dL. At first, a newborn with PKU will require weekly blood testing to tweak the diet, as babies grow very fast. As the child grows and the dietary intervention becomes more stable, phe levels are checked every month to every three months to be sure the diet is being followed as desired. Teaching children about PKU, their diet, and phe levels early-on may help children to accept that the low phe diet is their way of life.
References
- "Nutrition Management of Patients with Inherited Metabolic Disorders"; Acosta, Phyllis; 2010
- Newborn Screening; 'The Screening, Technology And Research in Genetics'; (STAR-G) Project
