This document summarizes the catabolism of phenylalanine and tyrosine. It discusses that phenylalanine is an essential amino acid that is converted to tyrosine. Tyrosine can then be incorporated into proteins or used to synthesize important compounds like catecholamines, thyroid hormones, and melanin. It also describes disorders that can occur if there are defects in the metabolic pathways of phenylalanine and tyrosine, including phenylketonuria (PKU), tyrosinemia types 1 and 2, and albinism. PKU is caused by a deficiency of phenylalanine hydroxylase and causes accumulation of phenylalanine that can lead to intellectual disability if left untreated.