Revisiting the role of factor H in age-related macular degeneration: insights from complement-mediated renal disease and rare genetic variants.

Ophthalmologists are long familiar with the eye showing signs of systemic disease, but the association between age-related macular degeneration (AMD) and abnormal complement activation, common to several renal disorders, has only recently been elucidated. Although complement activation products were identified in drusen almost three decades ago, it was not until the early 21st century that a single nucleotide polymorphism in the complement factor H (FH) gene was identified as a major heritable determinant of AMD, galvanising global efforts to unravel the pathogenesis of this common disease. Advances in proteomic analyses and familial aggregation studies have revealed distinctive clinical phenotypes segregated by the functional effects of common and rare genetic variants on the mature protein and its splice variant, FH-like protein 1 (FHL-1). The predominance of loss-of-function, N-terminal mutations implicate AMD as a disease of general complement dysregulation, offering several therapeutic avenues for its modulation. Here, we explore the molecular impact of these mutations/polymorphisms on the ability of variant FH/FHL-1 to localise to polyanions, pentraxins, pro-inflammatory triggers, and cell surfaces across ocular and renal tissues and exert its multimodal regulatory functions, and their clinical implications. Finally, we critically evaluate key therapeutic and diagnostic efforts in this rapidly-evolving field.