Age-related macular degeneration: a new viewpoint

Age-related macular degeneration (AMD) is a major cause of blindness in the United States. AMD can be categorized into an atrophic (dry) form and a neovascular (wet, exudative) form. The atrophic form involves alterations of pigment distribution, loss of RPE cells and photoreceptors and diminished retinal function due to an overall atrophy of the cells. The neovascular AMD involves proliferation of abnormal choroidal vessels, which penetrate the Bruch's membrane and RPE layer into the subretinal space, thereby forming extensive clots and/or scars. Both environmental and genetic factors are suspected to play a role in AMD. Despite extensive genetic screening of candidate genes only two associations have been identified with AMD (Adenosine triphosphate (ATP)-binding cassette rim (ABCR) protein and apolipoprotein E gene-ApoE). The ABCR protein is retinal specific and accounts for only 3% of AMD cases. ApoE is not specific to the retina, and has been more intriguingly associated with Alzheimer's, another disease of age. The most consistent major risk factor in AMD is age. Our studies on the ACE gene show an association of protection with an Alu element insert, which might be affecting the level of the ACE gene. The ApoE 4 allele and the ACE Alu+/+ genotype have both been shown to be a risk for Alzheimer's and protective for AMD. Given these recent genetic associations, we should examine possible common pathways in diseases of age and their interaction with human genetic polymorphisms.