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Treatment variables and intellectual outcome in children with classic phenylketonuria. A single-center-based study
1Section of Neurology, St. Christopher's Hospital for Children, Temple University School of Medicine, Philadelphia, Pennsylvania 19134.
Insights
Early and sustained phenylalanine-restricted diets improve intellectual outcomes for children with phenylketonuria (PKU). Continuous dietary management through age 12 is crucial for the best intellectual prognosis in PKU patients.
Area of Science:
- Metabolic disorders
- Neurodevelopmental outcomes
- Genetics and personalized medicine
Background:
- Classic phenylketonuria (PKU) is a genetic metabolic disorder.
- Early intervention with a phenylalanine-restricted diet is standard treatment.
- Long-term intellectual outcomes are influenced by diet adherence and timing.
Purpose of the Study:
- To identify treatment variables impacting intellectual outcomes in PKU patients.
- To analyze the relationship between diet initiation, duration, and IQ.
- To determine predictors of intellectual decline after diet discontinuation.
Main Methods:
- Retrospective analysis of 46 classic PKU patients.
- Categorization into three groups based on diet start and cessation timing.
- IQ testing during diet and follow-up testing after diet cessation.
Main Results:
- Patients starting diet before 3 months and continuing longer had higher IQs.
- IQ significantly decreased in one group after diet cessation.
- Predictors of IQ included age of diet initiation, phenylalanine levels, and diet control duration.
Conclusions:
- Early initiation and sustained phenylalanine-restricted diet until age 12 optimizes intellectual prognosis in PKU.
- Age at diet cessation and phenylalanine control are critical factors.
- Long-term adherence to dietary management is essential for cognitive development in PKU.
Abstract:
Records of 46 patients with classic phenylketonuria (PKU) were used to determine treatment variables associated with intellectual outcome. Patients comprised three groups: phenylalanine-restricted diet started 1) after 3 months and loss of diet control at a mean age of 7 years, 2) before age 3 months and loss of diet control at a mean age of 5 years, and 3) before age 3 months and through a mean age of 11 years. All underwent IQ testing during the diet; groups 1 and 2 were retested at a mean of six years off the diet. On the diet, groups 2 and 3 had higher IQs than group 1; group 3 IQ was also higher than IQ off diet in groups 1 and 2. After discontinuing the diet, group 2 IQs decreased significantly. Predictors of IQ in group 1 were age at loss of diet control and percentage of phenylalanine concentrations > 15 mg/dL; in group 2, mean phenylalanine concentrations and age at loss of diet control. Predictors of changes in group 1 IQs were global degree of dietary control and percentage of phenylalanine concentrations > 15 mg/dL; in group 2, phenylalanine concentrations of < 3 mg/dL and age at start of diet. Group 1 patients with phenylalanine concentrations < 3 mg/dL or > 15 mg/dL achieved no IQ gain by continuing the diet after age 7 years. Thus, intellectual prognosis is best for PKU patients who start a phenylalanine-restricted diet early and continue through age 12 years.