Phenylketonuria, or "PKU" for short, is a genetic disorder caused by a mutation. Phenylketonuria is a frameshift mutation, inherited, and makes amino acids called "Phenylalaine" to build up in the human body and also, where the term "Phenylketonuria" comes from. PKU is extremely rare and has less than 20,000 cases a year. Phenylketonuria is recessive and is a autosomal trait. The mutation comes from a person's diet and the certain foods they eat.