We profiled relevant gene family members across cell types in both Ctrl and KC samples, and found that almost all collagen genes were enriched in stromal cells and several genes were down-regulated in KC samples, such as COL5A1, COL5A3, COL10A1 and COL15A1 (Fig. 2d), which explained the decreased collagen lamellae and fibers in keratoconus39. This evidence concerns the gene COL15A1 and keratoconus.