Dietary
special formula.
A special formula is prescribed for individuals with tyrosinemia type 1. These formulas do not contain the amino acids phenylalanine and tyrosine. Foods with limited amounts of phenylalanine and tyrosine are provided. By itself, dietary treatment is not very effective in preventing the liver, kidney, and neurologic problems associated with tyrosinemia.
DIETARY MANAGEMENT.
The goal of dietary management of tyrosinemia is to provide a nutritionally complete diet with controlled intakes of phenylalanine and tyrosine.
A special formula that has little to no phenylalanine or tyrosine is necessary.
Because every child has a different “tolerance” of tyrosine and phenylalanine, dietary management is individualized. Physicians and nutritionists work with each family to develop a formula and food pattern that maintains plasma tyrosine levels below 500 µmol/L and plasma phenylalanine levels in the normal range (30-80 µmol/L).
Because the amount of phenylalanine and tyrosine that an individual needs changes with growth and during times of illness, monitoring by professionals who have experience with the dietary management of tyrosinemia is necessary.
INITIATION OF TREATMENT AND MONITORING.
A low-phenylalanine, low-tyrosine diet should be started immediately upon diagnosis. A low-tyrosine, low-phenylalanine formula (e.g., Tyros 1â or Tyrex-1â) is prescribed. The preparation of the formula also includes carefully measured amounts of a standard infant formula (e.g., Enfamilâ or Similacâ). Nitisinone therapy is also started at the time of diagnosis.
Goals of dietary management for infants and children are to:
- Support an appropriate rate of growth
- Support normal intellectual development
- Maintain optimal nutritional status
- Provide adequate nourishment
- Prevent neurological crisis
- Prevent liver and renal function problems
- Prevent formation of tyrosine crystals in the eyes (this occurs with elevated plasma tyrosine levels)
Adequacy of therapy is monitored by frequent measurement of:
- Plasma phenylalanine and tyrosine
- Plasma or urine concentrations of succinylacetone
- All plasma amino acids (to assure the adequacy of intake and to prevent deficiencies)
- Albumin, prealbumin, hematocrit, and hemoglobin (as measures of the overall adequacy of the diet)
- Liver function studies
To support typical growth for children with tyrosinemia, intakes of energy (calories), protein, carbohydrate, fat, vitamins, and minerals are carefully monitored.
MEETING NUTRIENT REQUIREMENTS.
For infants and young children with tyrosinemia, nutrient requirements are met using a combination of metabolic formula, breastmilk or infant formula, and/or natural foods.
The initial diet for treatment of tyrosinemia is based on the age, weight, and general health status of the infant. It is essential to initiate treatment (i.e., eliminate tyrosine and phenylalanine and provide adequate energy and total protein) as soon as the diagnosis is established. Blood levels of phenylalanine and tyrosine must be carefully monitored.
As the infant matures, small amounts of solid foods are introduced. The formula mixture should continue to contribute 75-80% of the child’s total nutrient intake. Throughout childhood the diet must be monitored carefully and adjusted regularly based on plasma phenylalanine and tyrosine levels, growth, weight gain, and recorded intakes of phenylalanine, tyrosine, protein, and energy from foods.
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