For example, microarrays have been instrumental in genomewide association scans that discovered an intronic SNP in complement factor H (CFH) causing age related macular degeneration [12], and a non synonymous SNP in IL23R – a gene encoding a subunit of a proinflammatory cytokine interleukin-23 receptor – that confers susceptibility to Crohn's disease [13]. The gene discussed is CFH; the disease is age-related macular degeneration.