PAH(Phenylalanine hydroxylase) is a member of the biopterin-dependent aromatic amino acid hydroxylase protein family. PAH plays a crucial role in converting phenylalanine to tyrosine, serving as the rate-limiting enzyme in phenylalanine catabolism. This enzymatic function is vital for proper metabolism of amino acids and prevention of toxic phenylalanine accumulation, which can lead to serious neurological issues. Deficiency in PAH activity leads to phenylketonuria (PKU), an autosomal recessive disorder characterized by cognitive impairment if not managed with a low-phenylalanine diet from an early age. Various mutations in PAH can result in decreased enzyme activity, leading to different severities of PKU, and while multiple isozymes of PAH have been reported, these are likely allelic variants that produce protein subunits with slightly different charges and electrophoretic migration patterns.