Molecular Basis Of Phenylketonuria In China

Classical phenylketonuria(PKU) is an autosomal recessive disorder caused by a deficiency of hepatic phenylalanine hydroxylase(PAH). The disease is characterized by hyperphenylalanemia, an accumulation of phenylalanine in serum, and associated abnormalities in aromatic amino acid metabolism. If left untreated, PKU patients will develop potential brain damage and irreversible mental retardation. PKU is the most common inborn error of amino acid metabolism, with an average incidence of 1 in 16,000 newborn children and a carrier frequency of 1 in 65 in China. Since dietary treatment is not readily available for most affected Chinese PKU families at present and gene diagnosis by linkage analysis is hampered by low incidence of heterogeneity of RFLP sites at the gene locus in the population, direct detection of PKU mutant alleles is the only alternative way to effective gene diagnosis.The current studies aimed at a systematic investigation of the molecular basis of PKU in the Chinese population. We began by using huamn PAH cDNA as probe to examine eight RFLP sites at the PAH gene locus in 55 Chinese PKU families. Seventeen RFLP haplotypes, including two new ones, were defined in this sample group. Haplotype 4 stands out as the most common one in both normal chromsomes (67.3%) and PKU chromosomes (78.2%), which reemphasized the nature of little heterogeneity of RFLPs at the PAH gene locus in Chinese. Various PCR-mediated sequencing techniques were then applied to identify sequence variations in exon-containing regions of the PAH gene in PKU patients. Eleven single base substitutions were characterized, 9 of which involved coding sequences and 2 in splice consensus sequences. Two of these 11 mutations are associated with CpG dinuceotide changes. Pattern of Mendelian transmission for all 11 mutations in proband families were verified using allele-specific oligonucleotide probe hybridization. Screening for each of these mutations in our PKU sample populations as contrasted to other populations indicate that altogether these mutations account for 72% of all PKU alleles in Chinese, 54% in Japanese, 55.2% in Koreans, and 0% in Caucasians. Several mutations demonstrate frequency difference in PKU samples...