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Effect on intelligence of relaxing the low phenylalanine diet in phenylketonuria
I Smith1, M G Beasley, A E Ades
1Department of Child Health, Institute of Child Health, London.
Insights
Early treatment for phenylketonuria (PKU) is crucial. High phenylalanine levels negatively impact intellectual progress in children, with IQ declining as phenylalanine concentrations rise, especially between ages 5-8.
Area of Science:
- Neuroscience
- Pediatrics
- Metabolic Disorders
Background:
- Phenylketonuria (PKU) is a genetic disorder requiring early intervention.
- Children with PKU treated early show intellectual deficits by age 4.
- Intellectual quotient (IQ) declines with increasing phenylalanine levels in PKU patients.
Purpose of the Study:
- To examine the association between intellectual progress and phenylalanine control in early-treated PKU children from ages 4 to 14.
- To assess how phenylalanine concentrations impact IQ at different developmental stages.
- To compare these associations across two birth cohorts with different diagnostic and management timelines.
Main Methods:
- Prospective follow-up of 599 children with early-treated PKU.
- Utilized multiple regression analysis to assess IQ changes in relation to phenylalanine levels.
- Controlled for confounding factors including previous IQ, phenylalanine control, social class, and diagnostic/management factors.
Main Results:
- A rise of 300 mumol/l in average phenylalanine levels between ages 5-8 corresponded to a 4-6 point drop in IQ at age 8.
- This IQ decline was less pronounced than the 7-10 point drop observed at age 4 for a similar phenylalanine increase.
- The association between phenylalanine control and IQ persisted up to age 10 in the later birth cohort (born 1972-1978), but disappeared after age 8 in the earlier cohort (born 1964-1971).
Conclusions:
- Maintaining controlled phenylalanine levels is critical for intellectual development in children with PKU throughout childhood.
- The impact of phenylalanine control on IQ may vary depending on the era of birth and associated management strategies.
- Continued monitoring and effective management of phenylalanine levels are essential for optimizing cognitive outcomes in individuals with PKU.
Abstract:
A total of 599 children with phenylketonuria, who had been treated early, were followed up prospectively in order to examine the association between intellectual progress from 4 to 14 years of age and control of phenylalanine concentrations. The phenylalanine rose from around 400 mumol/l during the first four years to above 900 mumol/l by 12 years. The children were divided into two cohorts: cohort I comprised 224 children born in the United Kingdom between 1964 and 1971 and cohort II 375 children born between 1972 and 1978. In a previous study it was shown that by 4 years of age these children already had a mean intelligence quotient (IQ) over half a standard deviation below general population norms, and that IQ fell linearly as average phenylalanine concentrations rose. Multiple regression was used to estimate the size of the associations between IQ at later ages and average phenylalanine concentrations in the periods between assessments, after controlling for previous IQ and phenylalanine control, social class, type of phenylketonuria, and factors relating to diagnosis and early management. For each 300 mumol/l rise in average phenylalanine concentrations for those aged 5 to 8 years IQ at 8 years fell by 4-6 points. This compared with a 7-10 point fall in IQ at 4 years for a similar rise in phenylalanine. After 8 years of age the association between IQ and phenylalanine control disappeared in cohort I but persisted in cohort II and was significant up to 10 years of age, although the association was smaller than at 8 years.