The infant two-disease screen is for phenylketonuria and congenital hypothyroidism. Congenital hypothyroidism is an endocrine disease characterized by mental retardation and poor physical development in newborns due to inadequate production of the thyroid hormones T3 and T4. Phenylketonuria is a congenital disorder of abnormal phenylalanine metabolism, and mental retardation is a prominent feature of this disease. Both disorders are congenital disorders and are among the few congenital disorders that can be diagnosed and treated early. Both diseases can have serious consequences if not diagnosed and treated in a timely manner, which is why the State requires that infants be screened for both diseases.