STX3 and microvillus inclusion disease: Erosion of the brush border, accumulation of subapical PAS-positive vesicles, the presence of ectopic microvilli (within MVI and basolaterally), and enlarged lysosomal organelles observed in duodenal biopsies from patients are all typical features of MVID, an autosomal recessive disorder known to be caused by variants in MYO5B (11), STX3 (18), and STX2BP (27), 3 genes encoding functionally and spatially related proteins that coordinate apical membrane trafficking in enterocytes.