How do a person get PKU?

Phenylketonuria (PKU) is an inherited metabolic disorder caused by a mutation in the gene responsible for producing the enzyme phenylalanine hydroxylase. This enzyme is necessary for breaking down the amino acid phenylalanine, which is found in many protein-containing foods. PKU is inherited in an autosomal recessive pattern, meaning that a person must receive two copies of the mutated gene, one from each parent, to develop the condition. If both parents are carriers of the PKU gene mutation, there is a 25% chance with each pregnancy that their child will have PKU.