RFLPs of the phenylalanine hydroxylase gene in the Italian population

Haplotype distribution and molecular defects at the phenylalanine hydroxylase locus in Italy

In order to investigate the molecular basis of phenylketonuria (PKU) in Italy, we characterized the RFLP haplotypes at the phenylalanine hydroxylase gene in 38 unrelated Italian PKU families. The distribution of haplotypes associated with PKU alleles differs from that of other European populations. In particular, haplotypes 1 and 6 are present in 39.7% and 17.6% of the PKU chromosomes, whereas the frequencies of haplotypes 2 and 3 are 5.9% and 2.9%, respectively. The characterization of PKU mutations using the polymerase chain reaction and allele-specific oligonucleotides shows that 1 out of 2 haplotypes 3 carries the splicing mutation and that 2 out of 4 haplotypes 2 carry the missense mutation associated with these haplotypes in North European populations. Our results indicate that the two molecular defects most frequent in Northern Europe represent a minority of PKU mutations in Italy.

Heterogeneity of phenylketonuria at the clinical, protein and DNA levels

The cloning of the phenylalanine hydroxylase gene and cDNA has potentially allowed the complete characterization of patients with phenylketonuria and already many mutations have been defined. Parents of patients now have the option of prenatal diagnosis. The 18 mutations defined so far indicate enormous heterogeneity not only within particular populations but also between populations. These mutations give little indication as to the locations of the amino acid residues important in enzyme function but one-third of the mutations are in exon 7 which may be indicating the importance of the region coded by this exon in the protein.