The Biochemical and Genetic Architecture of Geographic Atrophy: The Role of the FHL-1/CFH Axis and the Paradigm of RNA Interference Therapeutics

Geographic atrophy (GA) represents the advanced, non-neovascular (dry) form of age-related macular degeneration (AMD), a chronic, progressive, and currently irreversible neurodegenerative disease of the retina. The clinical consequences of GA are severe; it is characterized by the insidious, expanding loss of the retinal pigment epithelium (RPE), the overlying photoreceptors, and the underlying choriocapillaris. This state of complete RPE and outer retinal atrophy (cRORA) permanently destroys the neural architecture required for high-acuity central vision. For decades, the pathophysiological etiology of geographic atrophy was framed principally in terms of cumulative oxidative stress, lipid peroxidation, and cellular senescence. However, the foundational understanding of AMD pathophysiology changed substantially following the landmark genomic discoveries published in 2005. Multiple independent genome-wide association studies (GWAS) linked specific single-nucleotide polymorphisms in the CFH gene to a substantially increased risk of developing AMD. The CFH gene encodes Complement Factor H (FH) and its alternative splice variant, Factor H-like protein 1 (FHL-1), which are the primary soluble regulators of the alternative complement pathway. This genetic discovery established GA not merely as a disease of metabolic wear-and-tear, but fundamentally as an immunologic disorder driven by the chronic dysregulation of the innate immune system. With the rapid emergence and clinical validation of targeted gene-silencing technologies, particularly small interfering RNA (siRNA) and antisense oligonucleotides, there is substantial scientific and pharmaceutical interest in modulating the complement cascade at the post-transcriptional level. This narrative review examines the structural biology, spatial partitioning, and pathophysiological roles of the FHL-1/CFH axis in GA focusing on the possibilities of using siRNA as a new potential therapy for GA.