Primary (metabolic) aminoacidopathies Phenylketonuria (PKU). Classic PKU is inherited as an autosomal recessive trait. It is uncommon in Asians and African Americans and is due to deficiency of a liver enzyme known as “phenylalanine hydroxylase,” which is needed to convert the amino acid phenylalanine to tyrosine. With its major utilization pathway blocked, phenylalanine accumulates in […]