Abstract
Early-treated children with PKU are protected from mental retardation. However, recent studies have found IQ loss in these children, especially after termination of the low phenylalanine diet. We have studied IQ and IQ change in 91 early-treated children with PKU and 29 untreated or partially treated children with mild hyperphenylalaninemia (MH) who have been followed for up to 22 years. Their most recent psychological evaluations were compared to similar assessments done 5 years previously. In children with PKU, age (10.8 ± 4.7 yrs.) was negatively correlated with IQ (mean IQ = 98.4 ± 16.7) (r=-.30, p=.002). With age controlled, the treatment variable that best predicted IQ was the percent of blood phenylalanine levels ≥ 16 mg/dl while on diet (r2=0.86). These results suggest that IQ is significantly affected by dietary control during treatment. Over a 5 year period, mean IQ changes were -4.3 ± 14.8 in children with PKU off-diet, +7.4 ± 14.1 in children with PKU on-diet, and +2.8 ± 10.5 in children with MH. IQ change did not correlate with IQ score. With age controlled, the best predictor of IQ loss was diet discontinuation (r2=.159); natural (pre- or post-diet) blood phenylalanine level was the second best predictor (r2=.083). This suggests that loss of IQ is greater in children who have terminated the diet, particularly in those with higher natural blood phenylalanine levels. These findings may have implications for the issue of diet continuation or discontinuation during school age years.
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Waisbren, S., Mahon, B. & Levy, H. 1273 PREDICTORS OF IQ AND IQ LOSS IN TREATED PHENYLKETONURIA (PKU). Pediatr Res 19, 323 (1985). https://doi.org/10.1203/00006450-198504000-01297
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DOI: https://doi.org/10.1203/00006450-198504000-01297