Phenylketonuria, or PKU, is a genetically inherited birth defect that causes an unwanted buildup of the amino acid phenylalanine in the blood. This buildup occurs because the enzyme that routinely converts one amino acid, phenylalanine, to another amino acid, tyrosine, is absent or deficient. Phenylalanine then accumulates in the blood and is toxic to brain tissue.
PKU at Birth
Babies born in the United States are screened for PKU with a blood test so treatment can begin immediately and prevent the adverse side effects of the condition, such as declining intelligence, neurological deterioration, stunted growth, hyperactivity and seizures. A treatment team typically consists of a metabolic dietitian, physician, geneticist and psychologist as an infant is monitored during different phases of growth and development in childhood to an adult.
A strict diet limited in phenylalanine is the main treatment for PKU. Phenylalanine is found in most protein-containing foods such as milk, eggs, cheese, nuts, soybeans, chicken, beef, pork, beans and fish. "Infants with PKU rely on formula for the first year of life just like any other infant, but in their case, it's not just any regular formula," says Kristi King, MPH, RDN, LD, CNSC, a spokesperson for the Academy of Nutrition and Dietetics. "They must rely solely on a special metabolic formula that is phenylalanine-free." However, some breast milk can be used in limited amounts.
Creating an Unique Meal Plan
As the infant grows and becomes developmentally ready for solid foods, a registered dietitian nutritionist with expertise in PKU will create a unique menu for the child. "Providing adequate calories, nutrients, vitamins and minerals is essential for child growth and development," says King. "A metabolic dietitian can help the patient and family develop meal plans that work for them that still provide all the essentials, including low-phenylalanine and high-tyrosine foods." Because so many foods are off limits with PKU, the meal plans include special formulas that are often the primary source of calories and essential nutrients. Special phenylalanine-free foods are available for children and teens with PKU. The metabolic dietitian will create individual eating plans and modify them as needed to promote healthy growth and development.
The diet needs to be followed for life. "Following a PKU-friendly diet is essential in order to maintain serum phenylalanine levels that are checked during routine blood draws," says King. "Having high serum phenylalanine levels can cause lack of concentration, shortened attention span and memory difficulties." In conjunction with blood monitoring, the metabolic dietitian will regularly review diet records or food journals and growth charts, making adjustments to the eating plan as needed.
Parents of children with PKU need to be creative with foods and use available PKU cookbooks. Get help with menu planning from the metabolic dietitian and plan ahead for eating out, school lunches, potlucks, trips and vacations, and other special events. Try to center special occasions around activities rather than food, and encourage your child to be part of the management of his or her diet as early as possible.