Article
Wechsler subscale IQ and subtest profile in early treated
phenylketonuria
P V Griffithsa, C Demellweekb, N Fayd, P H Robinsone, D C Davidsonc
a Department of
Psychology, University of Stirling and Royal Hospital for Sick
Children, Glasgow G3 8SJ, UK, b Roald Dahl EEG Unit, Alder Hey Hospital,
Liverpool L12 2AP, UK, c Department of Paediatrics, Alder Hey Hospital, d Department
of Psychology, University of Glasgow, Glasgow G12 8QF, UK, e Metabolic Disease Clinic, Royal Hospital for
Sick Children, Glasgow
Correspondence to: Dr P V Griffiths, Department of Psychology, University of Stirling, Stirling FK9 4LA, UK email: pvg1{at}stir.ac.uk
Accepted 3 November
1999
AIM
Mildly depressed
IQ is common in treated phenylketonuria. This study explored whether a
particular intellectual ability profile typifies early and continuously
treated phenylketonuria and whether component skills comprising the IQ
relate to socioeconomic and treatment factors.
METHODSIQ scores were
collected retrospectively from variants of the "Wechsler intelligence
scale for children" performed at age 8 on 57 children with early
treated, classic phenylketonuria. The mental ability pattern underlying
IQ was investigated by analysing subscale and subtest scores and
dietary factors, such as historical phenylalanine blood concentrations.
RESULTSThe
children's mean full scale IQ of 91.11 was significantly below the
healthy population norm. There was a significant discrepancy between
their mean verbal IQ (94.65) and mean performance IQ (89.42), suggestive of a spatial deficit, but the data did not support a
biochemical or sociological explanation. Individual Wechsler subtests
had no distinctive pattern. Phenylalanine control at age 2 was
predictive of overall IQ. At this age, children with annual median
phenylalanine < 360 µmol/litre (recommended UK upper limit) had a
mean IQ 10 points higher than those above.
CONCLUSIONSEarly and
continuous treatment of phenylketonuria does not necessarily lead to
normalisation of overall IQ. Verbal intelligence in the primary school
years appears to normalise if blood phenylalanine is maintained below
360 µmol/litre in infancy, but spatial intelligence may remain poor.
However, the discrepancy in skill development is not the result of
social status or treatment variables. Perhaps weak spatial intelligence
is an ancillary effect of a protective rearing style occasioned by the
dietary treatment regimen.
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Key messages
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Keywords: phenylketonuria; intelligence quotient; dietary treatment; policy
© 2000 by Archives of Disease in Childhood
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