[Progress in pathogenesis and therapeutic research in retinitis pigmentosa and age-related macular degeneration]

Retinitis pigmentosa (RP) and age-related macular degeneration (AMD) are designated special targeted eye diseases by the Welfare and Labor Ministry of Japan. We have been studying the pathogenesis, diagnosis, treatment, and evaluation of these diseases. The development of molecular genetic analyses of RP revealed that the type and frequency of mutations varied with the ethnic population. In our present study, we focused on the genetic analysis and clinical examinations for autosomal dominant retinitis pigmentosa (ADRP). We screened 96 unrelated ADRP families with 9 genes, which included rhodopsin, peripherin/RDS, RP 1, NRL, FSCN 2, PRPF 31, PRPC 8, HPRP 3, IMPDH 1. We also showed the correlations we have found between the phenotype and genotype of hereditary retinal diseases in Japanese patients. Our mutation screenings suggested that Japanese patients with ADRP might have a unique mutation, because the mutation in the FSCN 2 gene has been found only in Japanese patients. On the other hand, the Pro347Leu and Pro23His mutations in the rhodopsin, the Arg677X mutation in the RP 1, and the Asp226Asn mutation in the IMPDH 1 genes are representative mutations for ADRP, and are not found or are very rare in Japanese patients with ADRP. The results of randomized controlled trials of low-dose radiation for wet-type age-related macular degeneration located at the fovea centralis indicate the effectiveness of this treatment for maintaining visual acuity and regression of choroidal neovascular membrane (CNV) for at least one-year. Simple surgical removal of CNV or transplantation of autologous cultured iris pigment epithelium (IPE) with vitreous surgery showed some improvement of vision. In either RP or AMD, photoreceptors die, in most cases by apoptosis. Neurotrophic factors (NT) are effective for reducing these processes and preventing photoreceptor cell death in animal models. To apply these methods to humans, the procedures are as follows: 1) obtaining IPE by peripheral iridectomy, 2) culturing it with autologous serum and transfecting the cDNA of NT, and then 3) transplantation of these cells under the retina. We used cDNA of brain-derived neurotrophic factor (BDNF) with adeno-associated virus (AAV) as a vector. These ex vivo procedures were safe and very effective for preventing photoreceptor cell death in animal models, such as RCS rats and light-damaged rats. In the future, these procedures could be applied for RP or AMD and might show some clinical effects for maintaining or improving the vision of patients.