HTRA1 and age-related macular degeneration: AMD is the only complex disease for which 2 loci, CFH and ARMS2/HTRA1, explain a large proportion of risk (Edwards et al., 2005; Hageman et al., 2005; Haines et al., 2005; Klein et al., 2005; Dewan et al., 2006; Yang et al., 2006, p. 200; Swaroop et al., 2007; Deangelis et al., 2008; Fritsche et al., 2013).