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Intelligence and quality of dietary treatment in phenylketonuria
I Smith1, M G Beasley, A E Ades
1Department of Child Health, Institute of Child Health, London.
Insights
Early dietary intervention for phenylketonuria (PKU) improves intellectual progress. However, challenges in metabolic control mean many children still experience mild neurological impairment.
Area of Science:
- Metabolic Disorders
- Neurodevelopmental Pediatrics
- Genetics
Background:
- Phenylketonuria (PKU) is a genetic disorder requiring early dietary intervention.
- Long-term intellectual outcomes in PKU patients depend on treatment adherence and efficacy.
Purpose of the Study:
- To identify factors influencing early intellectual progress in children with PKU on a low-phenylalanine diet.
- To assess the impact of treatment timing and metabolic control on IQ scores.
Main Methods:
- Analysis of Phenylketonuria Register data from 1031 children born 1964-1980, with 808 followed prospectively.
- Comparison of intelligence quotient (IQ) scores across birth cohorts and treatment parameters.
Main Results:
- IQ scores improved over time for early-treated children, but plateaued in later cohorts.
- Delayed treatment and higher phenylalanine levels significantly correlated with lower IQ.
- Children with optimal treatment achieved IQ scores comparable to population norms.
Conclusions:
- Early initiation of a low-phenylalanine diet is crucial for intellectual development in PKU.
- Persistent mild neurological impairment suggests difficulties in fully controlling metabolic abnormalities.
Abstract:
The records of the Phenylketonuria Register were examined to determine the factors associated with early intellectual progress in children who had received a diet low in phenylalanine from soon after birth. A total of 1031 children were born between 1964 and 1980 and started treatment before they were 4 months of age, and 808 of them were followed up prospectively. In 263 children born between 1964 and 1971 (cohort 1), the mean intelligence quotient (IQ) at 4 years rose with year of birth from 24 points below revised IQ norms to 10 points below; in 545 born between 1972 and 1980 (cohort 2) there was no further rise in IQ and the mean remained eight points below the norms. IQ fell progressively by roughly four points for each four weeks' delay in starting treatment, for each 300 mumol/l rise in mean phenylalanine concentrations during treatment, and for each five months during the first two years during which phenylalanine concentrations were below 120 mumol/l. Forty six children in cohort 2 had the most favourable treatment characteristics. Their mean IQ, after standardising for social class, was 112.6, and similar to the mean for the same group estimated by multiple regression, and to revised population IQ norms for the period during which the children were tested. The data suggest that many children who are treated early continue to suffer a mild degree of neurological impairment because of the difficulties in fully controlling the metabolic abnormality.