Porphyrias: animal models and prospects for cellular and gene therapy.

The rapid progress in the development of molecular technology has resulted in the identification of most of the genes of the heme biosynthesis pathway. Important problems in the pathogenesis and treatment of porphyrias now seem likely to be solved by the possibility of creating animal models and by the transfer of normal genes or cDNAs to target cells. Animal models of porphyrias naturally occur for erythropoietic protoporphyria and congenital erythropoietic porphyria, and different murine models have been or are being created for erythropoietic and hepatic porphyrias. The PBGD knock-out mouse will be useful for the understanding of nervous system dysfunction in acute porphyrias. Murine models of erythropoietic porphyrias are being used for bone-marrow transplantation experiments to study the features of erythropoietic and hepatic abnormalities. Gene transfer experiments have been started in vitro to look at the feasibility of somatic gene therapy in erythropoietic porphyrias. In particular, we have documented sufficient gene transfer rate and metabolic correction in different CEP disease cells to indicate that this porphyria is a good candidate for treatment by gene therapy in hematopoietic stem cells. With the rapid advancement of methods that may allow more precise and/or efficient gene targeting, gene therapy will become a new therapeutic option for porphyrias.