Identifying Variable Number of Tandem Repeat Alleles in Phenylalanine Hydroxylase Gene in Patients with Phenylketonuria in Golestan Province, Iran

Background and Objective: Phenylketonuria (PKU) is a metabolic disorder that is caused by mutations in the phenylalanine hydroxylase (PAH) gene. The multiplicity of mutations in the PAH gene of PKU leads to the cases, in which the pathogenic mutation cannot be detected. In these cases, the variable number of tandem repeat (VNTR), which is the polymorphic marker associated with the PAH gene, is used to identify PKU carriers. The present study was conducted to investigate the allele frequency of this marker in PKU population of Golestan Province (north of Iran). Materials and Methods: In this cross-sectional descriptive study, 26 non-relative PKU patients (1-23 years old, phenylalanine: 4.5-250 mg/dl) were identified from different regions of Golestan Province within a one-year period (2016). Genomic DNA was then extracted from leukocytes using the high pure PCR template preparation kit (Roche) and the fragments containing the PAH VNTR were evaluated using PCR-sequencing method. Results: PCR products of PAH VNTR alleles produced 334, 454, 484, 514, and 604 bp fragments. They were corresponding to the presence of alleles with 3, 7, 8, 9, and 12 copies of the repeat units, respectively. In addition, the distribution of VNTR alleles was as follows: 28.85%, 28.85%, 17.3%, 19.23%, and 5.77%. Conclusion:  This study is the first report regarding the genetic structure of PKU population using PAH VNTR alleles in Golestan Province. Considering the population diversity in Iran, it is necessary to investigate the frequency and distribution of VNTR alleles in different parts of the country.