RFLP HAPLOTYPING AND MUTATION ANALYSIS OF THE PHENYLALANINE-HYDROXYLASE GENE IN DUTCH PHENYLKETONURIA FAMILIES

Restriction fragment length polymorphism haplotyping of mutated and no rmal phenylalanine hydroxylase (PAH) alleles in 49 Dutch phenylketonur ia (PKU) families was performed. All mutant PAH chromosomes identified by haplotyping (n=98) were screened for eight of the most predominant mutations. Compound heterozygosity was proven in 40 kindreds. Homozyg osity was found for the IVS12ntl mutation in 5 families, and for the R 158Q and IVS10nt546 mutations in one family each. All patients from th ese families suffer from severe PKU, providing additional proof that t hese mutations are deleterious for the PAH gene. Genotypical heterogen eity was evident for mutant haplotype 1 (n=27) carrying the mutations R261Q (n=12), E280K (n=4, P281L (n=1) and unknown (n=10), and likewise for mutant haplotype 4 (n =30) carrying the mutations R158Q (n=13), Y 414C (n=1) and unknown (n=16). Mutant haplotype 3 (n=20), in tight ass ociation with mutation IVS12ntl, appeared to be in strong linkage dise quilibrium (LDE) with its normal counterpart allele (n=4). Mutant hapl otype 6 (n=4), in tight association with the IVS10nt546 mutation, show ed moderate LDE with its counterpart allele (n=1). The distribution of the mutant PAH haplotypes 1, 3 and 4 among the Dutch PKU population r esembles that in other Northern and Western European countries, but it is striking that mutant haplotype 2 and its associated mutation R408W is nearly absent in The Netherlands, in strong contrast to its neighb ouring countries.