Diarrhea in patients with MVID is associated with villus blunting, loss of microvilli on the apical membrane of enterocytes, the expansion of autophagic lysosomes, and loss of apical transporters, such as sodium/proton exchanger 3 (NHE3/SLC9A3), sodium-dependent glucose transporter 1 (SGLT1/SLC5A1), and peptide transporter 1 (PEPT1/SLC15A1) (6, 7). The gene discussed is SLC15A1; the disease is microvillus inclusion disease.