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Intelligence in mild atypical phenylketonuria
P M Costello1, M G Beasley, S L Tillotson
1Medical Unit, Institute of Child Health, London, UK.
Insights
Even mild phenylketonuria (PKU) can impact intelligence. Lowering blood phenylalanine (Phe) levels below 400 mumol/l in early childhood is crucial for cognitive development in children with PKU.
Area of Science:
- Biochemistry
- Pediatrics
- Neuroscience
Background:
- Phenylketonuria (PKU) is a genetic disorder affecting phenylalanine metabolism.
- Mild PKU cases have blood phenylalanine (Phe) levels below 900 mumol/l.
- The impact of Phe levels on cognitive development in mild PKU requires further investigation.
Purpose of the Study:
- To examine the relationship between blood Phe concentrations and intelligence in children with mild PKU.
- To determine if treatment and social class influence this relationship.
- To establish optimal Phe control targets for cognitive outcomes.
Main Methods:
- Studied 82 children with mild PKU (ages birth to 4 years).
- Assessed intelligence quotient (IQ) at age 4 using Stanford-Binet.
- Correlated average blood Phe levels with IQ, considering treatment status and social class.
Main Results:
- Mean IQs were below population norms in both treated and untreated children.
- IQ decreased by approximately 6 points for every 100 mumol/l increase in mean Phe levels.
- The Phe-IQ relationship was more pronounced in mild PKU than previously reported.
Conclusions:
- Blood Phe levels of 400 mumol/l or higher necessitate dietary intervention in mild PKU.
- Maintaining Phe levels below 400 mumol/l is recommended throughout early childhood.
- Early and consistent Phe control is vital for optimal cognitive development in all PKU forms.
Abstract:
In 82 children with mild phenylketonuria (PKU) (blood phenylalanine (Phe) concentrations consistently below 900 mumol/l throughout follow up) the relationship between intelligence at age 4 (IQ by Stanford-Binet) and average blood Phe concentrations from birth to 4 years was examined. Of the 82 children 24 had received no treatment. In the group as a whole, and in the 24 untreated subjects alone, mean IQs were significantly below population norms, with deficits of approximately 4.5 points and 9 points respectively. After allowing for social class IQ fell progressively by approximately 6 points for each 100 mumol/l rise in mean Phe concentrations in both the treated and untreated subjects. This relationship resembled that previously reported in early treated children with more severe forms of PKU, except that the scale of the relationship was even greater. We conclude that all children whose blood Phe concentrations reach 400 mumol/l or above should receive a low Phe diet, at least during the preschool years, and that the aim should be to control blood Phe levels below 400 mumol/l throughout early childhood in all forms of PKU.