Phenylketonuria (PKU) is an inherited metabolic disorder caused by an absence or deficiency of the enzyme phenylalanine hydroxylase (PAH). The disorder is easily detectable via routine newborn screening and treatment usually begins immediately.
PAH is responsible for processing the enzyme phenylalanine, one of the amino acids vital for normal growth and development. In individuals with PKU, PAH fails to convert phenylalanine into tyrosine leading to an accumulation of toxic phenylalanine in the blood and brain. The direct toxic effect of phenylalanine can lead to severe intellectual disability and other symptoms.