This invention provides a range of translatable polynucleotide and oligomer molecules for expressing a human phenylalanine hydroxylase (PAH), or a fragment thereof having PAH activity. The polynucleotide and oligomer molecules are expressible to provide the human PAH or a fragment thereof having PAH activity. The molecules can be used as active agents to express an active polypeptide or protein in cells or subjects. The agents can be used in methods for ameliorating, preventing, delaying onset, or treating a disease or condition associated with phenylketonuria, decreased metabolism of phenylalanine, or increased levels of phenylalanine in a subject.