In damaged mucosa, long crypt basins can be misread as villi in H&E staining (Figures 3D, G), but with the aid of APOA4 staining (Figures 3E, H), it can be seen that the crypt extends up close to the lumen, resulting in a histological diagnosis of total villous atrophy in both cases. This evidence concerns the gene APOA4 and Atrophy.