Phenylketonuria (PKU) is an inherited metabolic disorder that occurs in individuals who carry a homozygous mutation in the gene responsible for producing the phenylalanine hydroxylase enzyme. This condition follows an autosomal recessive inheritance pattern. For a child to be affected by PKU, they must inherit a copy of the defective gene from both parents. If only one parent carries the faulty gene, their child will not develop PKU but has a 50% chance of being a carrier. Most often, PKU is passed on to children by parents who are asymptomatic carriers of the mutation and are unaware of their carrier status.