Investigation of exon 4 mutations of phenylalanine hydroxylase gene in phenylketonuria patients in Guilan Province using PCR-sequencing

Background: Phenylketonuria (PKU) is a heterogeneous and autosomal recessive metabolic disorder that is mainly caused by mutations in the hepatic phenylalanine hydroxylase (PAH) gene. Distribution pattern of mutations in the PAH gene are specific to each population. To date, no reports of phenylketonuria molecular analysis have been found in this population. The aim of this study was to identify PAH mutations within exon 4 in PKU patients in Guilan Province and compare it with the studies in other parts of Iran. Materials and Methods: In this cross-sectional and descriptive study, 25 unrelated PKU patients (age range, 1-21 years) were identified from different regions of Guilan Province during a one-year period. After collecting blood samples and DNA extraction, the DNA fragments containing the exon 4 of the PAH gene and its flanking intronic sequences were amplified and sequenced. Results: In this study, IVS4+5G>T mutation (10%) was identified. This mutation was found in two homozygous PKU patients and one heterozygous patient; they had mPKU and cPKU phenotypes, respectively and their parents were third degree relatives. In addition, IVS4+47C>T (28%) and IVS3-22C>T (8%) polymorphisms were also detected. Conclusion: Investigation of mutations in the PAH gene can be a useful tool for molecular detection of the PKU disease and carrier detection in this population. Moreover, the other 12 remaining exons need to be analyzed to obtain the full spectrum of mutations of this gene among the PKU patients in Guilan Province