PKU is a monogenic autosomal recessive disease caused by different LoF mutations in the phenylalanine hydroxylase (PAH) gene located on chromosome 12 with a prevalence between 6.7 and 10 in 100,000 newborns (Woo et al., 1983; Gessler and Gao, 2016). The gene discussed is PAH; the disease is phenylketonuria.