The Pah KO mice is a phenylketonuria (PKU) disease model generated by knocking out the Pah gene in mice using gene editing techniques. In this model, both Pah mRNA and PAH protein expression are completely absent, leading to PKU-related phenotypes associated with impaired phenylalanine (Phe) catabolic metabolism. As blood Phe levels rise and Tyr levels decrease in the mouse, the pigmentation of their fur gradually fades, and by 8 weeks of age, their fur color becomes entirely brown. Consequently, Pah KO mice serve as valuable tools for studying the genetic mechanisms of PKU in humans and for the preclinical evaluation of therapeutic drugs.