of AMD. The authors of both papers consider their study to underscore the influence of the complement pathway in the pathogenesis of this disease. In two 2006 studies, another gene that has implications for the disease, called HTRA1 (encoding a secreted serine protease), was identified. Six mutations of the gene SERPING1 (Serpin Peptidase Inhibitor, Clade G (C1 Inhibitor), Member 1) are associated with AMD. Mutations in this gene can also cause hereditary angioedema. Fibulin-5 mutation: Rare forms of the disease are caused by genetic defects in fibulin-5, in an autosomal dominant manner. In 2004, Stone et al. performed a screen on 402 AMD patients and revealed a statistically significant correlation between mutations in fibulin-5 and incidence of the disease. Mitochondrial-related gene polymorphisms such as that in the MT-ND2 molecule, predicts wet AMD. Pathophysiology The pathogenesis of age-related macular degeneration is not well known, although some theories have been put forward, including oxidative stress, mitochondrial dysfunction, and inflammatory processes. The imbalance between the production of damaged cellular components and degradation leads to the accumulation of harmful products, for example, intracellular lipofuscin and extracellular drusen. Incipient atrophy is demarcated by areas of retinal pigment epithelium (RPE) thinning or depigmentation that precede geographic atrophy in the early stages of AMD. In advanced stages of AMD, atrophy of the RPE (geographic atrophy) and/or development of new blood vessels (neovascularization) result in the death of photoreceptors and central vision loss. In the dry (nonexudative) form, drusen accumulates between the retina and the choroid, causing atrophy and scarring to the retina. In the wet (exudative) form, which is more severe, blood vessels grow up from the choroid (neovascularization) behind the retina which can leak exudate and fluid and also cause hemorrhaging. Early work demonstrated a family of immune mediators was plentiful in drusen. Complement factor H (CFH) is an important inhibitor of this inflammatory cascade, and a disease-associated polymorphism in the CFH gene strongly associates with AMD. Thus an AMD pathophysiological model of chronic low grade complement activation and inflammation in the macula has been advanced. Lending credibility to this has been the discovery of disease-associated genetic polymorphisms in other elements of the complement cascade including complement component 3 (C3). A powerful predictor of AMD is found on chromosome 10q26 at LOC 387715. An insertion/deletion polymorphism at this site reduces expression of the ARMS2 gene though destabilization of its mRNA through deletion of the polyadenylation signal.