Exudative age related macular degeneration (ARMD) is linked with the CST3 gene, a study in Germany has found. The condition—an advanced stage of ARMD—is a leading cause of blindness among elderly western Europeans. There is evidence for a genetic cause but no consensus about a candidate gene.

Zurdel et al chose as a potential candidate the cystatin C gene—CST3—coding for a protease inhibitor common in tissues and body fluids which strongly inhibits cathepsins, including cathepsin S, and results in debris accumulating around retinal pigment epithelial cells. Extracellular deposits beneath the retinal pigment epithelium are one characteristic of early ARMD.

They characterised 167 patients with exudative ARMD and 517 unrelated controls for CST3 genotypes A/A, A/B, B/B by PCR and restriction endonuclease analysis. The controls were from Germany, Switzerland, Italy, and the United States to cover regional or ethnic differences in frequency of CST3 alleles.

CST3 genotype counts were significantly different for patients over controls, especially for CST3 B/ B genotype (odds ratio 2.97; 95% confidence interval 1.28 to 6.86). Allele frequencies A and B were similar between patients and controls and among controls from all locations. CST3 B/B was significantly linked with ARMD as shown by Kaplan-Meier analysis, with mean disease free survival time in pooled men and women for genotype A/A or A/B of 85 years and B/B 76 years.

CST3 B/B carries increased risk of exudative ARMD, conclude Zudel et al; cystatin C is therefore implicated in the disease process, though its exact role remains to be determined.