Interestingly, we did not detect any variants in two genes coding for the heterodimeric transporter, LAT1 (SLC7A5) and 4F2hc (SLC3A2), for which earlier studies showed that they could be potential modifiers of PKU phenotype [34], neither did we detect the intronic rs113883650 variant in the LAT1 (SLC7A5) gene which has been associated with increased concentration of brain phenylalanine in PKU patients with severe hyperphenylalaninemia as shown in a recent study [11]. This evidence concerns the gene SLC3A2 and phenylketonuria.