Mutation analysis of the PKU population in England and Scotland - how and why

To date, over 150 disease-causing mutations have been defined at the phenylalanine hydroxylase (PAH) locus. Because of their varied effects on enzyme activity as determined in in vitro expression systems, it is to be anticipated that different combinations would result in a continuum of phenotypes ranging from severe classical PKU to non-PKU hyperphenylalaninaemia requiring no dietary phenylalanine restriction. To examine this, it is essential to characterize the mutations on both alleles in as many affected individuals as possible. Using heteroduplex analysis with synthetic DNA constructs, we are able to characterize 14 different mutations in 3 exons (12, 3 and 7) of the PAH gene. In the PKU populations of England and Scotland, we have screened over 370 independent mutant chromosomes from 200 affected individuals or their parents. Analysis of these exons in conjunction with screening for two specific mutations in exon 2 and intron 10 enables us to identify the mutations on 60 to 65% of mutant chromosomes. These are found in 21 different combinations in 81 affected individuals in whom both mutations could be identified. Analysis of various parameters measuring the degree of dietary restrictions and management in these patients should give some indication whether genotype can be usedmore » as an independent predictor of the severity of the disorder.« less