Complement, Macular Degeneration Linked

Three new studies have linked a single nucleotide polymorphism is a complement protein, Factor H, to an increased risk of macular degeneration. Macular degeneration is the most common cause of vision loss in the elderly. All 3 studies appear were published online in the journal Science.

In the Texas study, 31.4 percent of the people with the disease had two copies of the variant gene, and 21.5 percent had no copies. In the control group without the disease, 13.7 percent had two copies of the variant and 42.6 percent had no copies. The rest, nearly half of both groups, had one copy of the variant.

So obvioulsy there must be other factors at work as well

Complement is a very basic, ancestral part of the immune response. It serves to mark invading organisms for uptake by specialized cells called phagocytes. It exists as far back as echinoderms, which include star fish and sea urchins. Basically, some complement proteins bind to "foreign cells" and activate either uptake by phagocytes or lysis of the cells. Factor H is expressed on the surface of host cells and downregulates the complement response. One can imagine that less active versions of Factor H could increase complement mediated damage to host tissues, such as the eye.

Other complement linked diseases include susceptibility to gram negative bacterial infections, particularly meningococcus, paroxysmal nocturnal hemoglobinuria and hereditary angioedema. In addition complement plays a big role in many autoimmune diseases such as lupus and dermatomyositis.

Knowing that complement is involved should lead to new avenues of treatment, presumably starting with inhibition of the complement system.