An artifact band frequently associated with variable number of tandem repeat marker at phenylalanine hydroxylase gene: application in carrier detection and prenatal diagnosis of phenylketonuria

The variable number of tandem repeat (VNTR) marker located at the 3′-end of the phenylalanine hydroxylase (PAH) gene, PAHVNTR marker, is commonly used in carrier detection and prenatal diagnosis of the PKU disease. During the molecular diagnosis of the disease, an artifact band associated with the PAHVTNR marker was frequently observed. Analysis of genotyping data from nine trios families indicated that in heterozygote individuals, the observed stutter (artifact) bands at PAHVNTR marker were minor bands with one repeat sequence shorter than the upper main bands. More investigations using sequencing revealed that the artifact band was associated with VNTRs including seven or higher core repeats. In statistical analysis, 75% of the studied heterozygote individuals represented PCR artifact band. The presence of the artifact band associated with PAHVNTR marker highlights a serious alarm risk of possible technical misdiagnosis in the application of the PAHVNTR marker in carrier detection and prenatal diagnosis of the PKU disease.