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126 ANALYSIS OF MUTANT PKU ALLELES IN THE POPULATION OF SOUTHERN POLAND

A sample of 22 PKU probands were screened for six mutations by polymerase chain reaction (PCR) amplification of their genomic DNA and hybridization with allele-specific-oligonucleotides. The following mutations were tested: exon 5, codon 158 (CGG-CAG); exon 7,codon 261 (CGA-CAA), codon 281 (CCT-CTT); exon 12,5' splice donor site (GT-AT), codon 414 (TAC-TGC) and codon 408 (CGT-TGG). Dot-blot hybridization with 32P labelled ASO was used to detect the presence of the mutations. Results: The analysis covered 44 mutant chromosomes from 22 unrelated PKU children. About 66% of PKU alleles studied were characterized by three distinct mutations: in codon 408, 158 and 261, with codon 408 (56.8%) being the most prevalent and tightly linked to haplotype (HT) 2. The codon 158 and 261 mutations were found in 6.8% and 2.3% of all PKU alleles, respectively. The missence mutation in codon 158 was detected in 2 patients who suffered from the classical form of PKU, and was linked to HT 4. The G to A transition in codon 261 was only found in a single chromosome and was linked to HT 1. No mutant PAH gene exhibiting the splicing defect in intron 12, neither the mutations in codon 414 and 281 was identified. Our results confirm molecular heterogeneity of PKU and show that the majority (66%) of all PKU alleles are characterized by three different mutations.