Termination of restricted diet in children with phenylketonuria: a randomized controlled study. Transitory hyperphenylalaninaemia in children with continuously treated phenylketonuria. Neuropsychological studies on adolescents with phenylketonuria returned to phenylalanine-restricted diets. Phenylalanine intakes of 1- to 6-year-old children with phenylketonuria undergoing therapy.
This study demonstrates the feasibility of a randomized controlled investigation of terminating the phenylalanine-restricted diet in four-year-old children with phenylketonuria. The parents of 14 of 16 children gave informed consent, knowing their children would be randomly assigned to either a diet-continuation or a diet-termination group. Compared with the continuation group, the mean serum phenylalanine of the termination group was 15.1 mg per dl higher (P less than 0.005) one year, and 9.2 mg per dl higher (P less than 0.025) two years after diet termination. Mean weight gain between four and six years of age was 3.4 kg greater in the terminated than in the continued group (P less than 0.01). There were no significant differences in mean head circumferences, height or performances on psychologic tests. At age six, mean I.Q. in the terminated group was 99.8, in those continuing the diet 103.6. Children in both groups showed some subtest scatter in memory and concentration. Thus, no harmful effects of diet termination were noted, but a longer period of observation in a larger number of subjects is needed. Cognitive and behavioral effects of temporarily challenging the CNS with elevated levels of phenylalanine in treated phenylketonuria (PKU) were investigated in a triple-blind, cross-over study. A high phenylalanine supplement was given over 3 months to sixteen 10- to 16-year-old early and continuously treated children with classical PKU. We used the WISC and Rivermead tests to measure cognitive function and the Rutter Scales to assess disordered behavior. Parents and children guessed at the condition imposed. The Group x Phase interaction for phenylalanine level was statistically significant, but this pattern was not mirrored in the psychological test data, and guessing was random. Results suggest that intellectual ability, memory, and conduct are not affected by medium-term hyperphenylalaninaemia in PKU after 10 or more years of treatment. Nine adolescents with phenylketonuria (PKU), who had been on unrestricted diets for 2 to 11 years, underwent serial neuropsychological testing over two consecutive 4- to 5-week periods during which each was maintained on a low-phe diet supplemented in a triple-blind fashion either with L-phe (high phe) or L-alanine (low phe). Assignment to the initial condition was done randomly, and the alternate condition was substituted at the end of the first 4- to 5-week period. In 6 of 7 subjects with PKU, baseline median choice reaction times (RTs) were slower than those of controls matched for age, sex, handedness, and Full-Scale IQ (WISC-R). A highly significant improvement occurred during the low-phe phases of the study. Results suggest that adolescents with PKU on unrestricted diets have a neuropsychological deficit that is out of proportion to their overall intellectual handicap. Moreover, this deficit appears to be at least partly reversible by return to dietary phe restriction despite years of hyperphenylalaninemia. Mean of median phenylalanine intakes of 1- to 6-yr-old treated phenylketonuria patients who were growing normally were evaluated by age, sex, and treatment group assignment. Total daily means of median phenylalanine intakes of subjects in treatment group 1 were significantly different from those of subjects in treatment group 2 except at the median age of 69 months. Total daily phenylalanine intakes varied from 285 +/- 10 to 453 +/- 30 mg (mean +/- SEM) by subjects in treatment group 1. Total daily phenylalanine intakes of subjects in treatment group 2 varied from 349 +/- 12 to 530 +/- 42 mg (mean +/- SEM). Mean, median phenylalanine intakes by males ranged from 30 mg/kg of body weight by the younger to 23 mg/kg of body weight by the older subjects. Means of median phenylalanine intakes of females varied from 32 mg/kg of body weight by the younger to 21 mg/kg of body weight by the older subjects. No child had a median phenylalanine intake below 10 mg/kg of body weight.
The results of non-randomised studies have concluded that a low-phenylalanine diet is effective in reducing blood phenylalanine levels and improving intelligence quotient and neuropsychological outcomes. We were unable to find any randomised controlled studies that have assessed the effect of a low-phenylalanine diet versus no diet from diagnosis. In view of evidence from non-randomised studies, such a study would be unethical and it is recommended that low-phenylalanine diet should be commenced at the time of diagnosis. There is uncertainty about the precise level of phenylalanine restriction and when, if ever, the diet should be relaxed. This should be addressed by randomised controlled studies.