HTRA1 and atrophic macular degeneration: HTRA1 enzyme activity was also linked to bone formation19,20, the degradation of β-amyloid and tau in Alzheimer’s disease21–23 and to regulation of tumor progression24–26, arthritis27–32, osteoporosis33 and the “wet” (neovascular) as well as “dry” (geographic atrophy) forms of age-related macular degeneration34–36.