This initial observation has been supported by additional histopathologic studies showing an increased BMP4 expression in retinal sections from donors with early AMD in the areas of RPE and the Bruch membrane directly adjacent to hard and soft drusen [48], whereas in control samples from patients without AMD the immunohistochemical expression of BMP4 was undetected in RPE. Here, BMP4 is linked to age-related macular degeneration.