Quality of dietary control in phenylketonuric patients and its relationship with general intelligence.

OBJECTIVES: Assessment of the quality of dietary treatment of phenylketonuria (PKU) patients and investigation of its relationship with the general intelligence of the patients.
METHODS: Cross-sectional and longitudinal study of 105 PKU treated patients. The index of dietary control (IDC) was calculated as the phenylalanine (Phe) data reduction in half-year medians and the mean of all medians throughout the patient's life. We calculated four different IDCs related to age: IDC-A (< 6 years), IDC-B (6-12 years), IDC-C (13-18 years) and IDC-D (> 18 years). To evaluate the fluctuation of Phe values we calculated the standard error of the estimate of the regression of Phe concentration over age. Development quotient was calculated with the Brunet-Lezine test (< 4 years). Intelligence quotient was evaluated with the Kaufman Bit Intelligence Test (K-Bit), Wechsler Intelligence Scale for Children-Revised (WISC-R) and Wechsler Adult Intelligence Scale Third Edition (WAIS III).
RESULTS: Cross-sectional study: The IDC in age groups were significantly different and so were the number of patients with good, acceptable and poor IDC related to age (p < 0.001). Sampling frequency was good in 72, acceptable in 23 and poor in 10 patients. The general intelligence (101 +/- 10) correlated negatively with the IDC (p < 0.0001) and Phe fluctuations (p < 0.004). Longitudinal study: Significant differences were observed between the IDC through the patients' lifetime except in the adolescent/adult period.
CONCLUSIONS: 85% of PKU patients showed good/acceptable quality of dietary control. General intelligence correlates with the IDC at all ages, which highlights the importance of good control to achieve good prognosis.