Accordingly, Spijker et al. found a significant increase in bihormonal insulin+/glucagon+ and NKX6.1+/amyloid+/glucagon+ cells upon analyzing mature β-cell markers (e.g., MAFA, FOXO1, NKX6.1) in human and non-human primate normal or T2D samples (Spijker et al., 2015). Here, MAFA is linked to type 2 diabetes mellitus.