Article
Effect of genotype on changes in intelligence quotient after
dietary relaxation in phenylketonuria and hyperphenylalaninaemia
Lindsey G Greevesa, Christopher C Pattersond, Dennis J Carsone, Ruth Thomb, Melanie C Wolfendenc, Johannes Zschockef, Colin A Grahamf, Norman C Nevinf, Elisabeth R Trimblea
a Royal Belfast
Hospital for Sick Children, Belfast BT12 6BE, UK, b Department of Dietetics, The
Royal Belfast Hospital for Sick Children, c Department of Clinical Psychology, Royal Belfast
Hospital for Sick Children, d Department
of Epidemiology and Public Health, Queen's University of Belfast,
Belfast BT12 6BN, UK, e Department of Child Health, Queen's University
of Belfast, f Department of
Medical Genetics, Belfast City Hospital, Belfast BT9 7AB, UK
Correspondence to: Professor E R Trimble, Department of Clinical Biochemistry, Royal Victoria Hospital, Grosvenor Road, Belfast, BT12 6BA, UK
Accepted 22 October
1999
BACKGROUND
Associations
between genotype and intellectual outcome in patients with
phenylketonuria are complicated because intelligence is influenced by
many variables, including environmental factors and other genetic
determinants. Intellectual changes with age, both on and after
relaxation of diet, vary within the patient population. This study aims
to determine whether a significant association exists between genotype
and change in intelligence after relaxation of diet.
METHODS125
patients with hyperphenylalaninaemia and phenylketonuria whose diet
was relaxed after 8 years of age. Verbal, performance, and full scale
intelligence quotients at 8, 14, and 18 years were expressed as
standard deviation scores (IQ-SDS), and genotype as predicted residual
enzyme activity (PRA) of phenylalanine hydroxylase.
RESULTSIQ-SDS
at 8, 14, and 18 years were significantly below normal; no association
was found between PRA and IQ-SDS. Significant reductions in verbal and
full scale IQ-SDS occurred between 8 and 14 years and 8 and 18 years.
There was a significant association between PRA and the reduction in
verbal, performance, and full scale IQ between these years. Multiple
regression analysis of 18 year results, using 8 year results as
covariates, supported the association between PRA and IQ-SDS; after
adjustment for phenylalanine control, both up to and after the age of 8 years, the full scale IQ-SDS at 14 and 18 years was 0.15 higher for
each 10% increase in PRA.
CONCLUSIONSGenotype
might be useful in predicting the likelihood of intellectual change in
patients with hyperphenylalaninaemia and phenylketonuria whose diet is
relaxed after the age of 8 years.
Keywords: mutation; predicted residual enzyme activity; phenylketonuria; intelligence quotient
© 2000 by Archives of Disease in Childhood
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This article has been cited by other articles:
-
National Institutes of Health Consensus Developmen,
(2001). National Institutes of Health Consensus Development Conference Statement: Phenylketonuria: Screening and Management, October 16-18, 2000. Pediatrics
108: 972-982
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