Phenylketonuria is an autosomal recessive genetic disorder caused by mutations in the phenylalanine hydroxylase gene, leading to reduced enzyme activity and resulting in the accumulation of phenylalanine and its metabolic products in the body, causing the disease. Phenylketonuria is the most common congenital amino acid metabolism disorder, clinically presenting with intellectual developmental delays, lighter skin and hair pigmentation, and a musty urine odor. The disease is mainly caused by mutations in the phenylalanine hydroxylase gene, leading to reduced enzyme activity.