HTRA1 and age-related macular degeneration: The presence of a Muller cell-specific regulatory region upstream of the HTRA1 promoter [40], and the upregulation of glial fibrillary acidic protein (GFAP) immunoreactivity in the Müller cells of donor retina with drusen [41] may be considered supporting evidence for the involvement of Muller glia in early stages of AMD.