Rab11 is a useful tool for the diagnosis of microvillous inclusion disease.

Microvillous inclusion disease (MVID) is a congenital condition presenting with intractable diarrhea. Biopsies demonstrate abnormal apical PAS and CD10 staining in surface enterocytes correlating with the presence of characteristic cytoplasmic inclusions. MVID has been linked to mutations in myosin Vb, important in apical membrane recycling. Rab11 associates with myosin Vb in vesicle membranes and is also integral in recycling plasma membrane components. The authors performed Rab11 immunostaining on biopsies from 7 MVID cases, 10 normal small intestines, and 10 with chronic enteritis. In MVID cases, Rab11 showed diffuse apical cytoplasmic staining of surface enterocytes in a pattern similar to PAS and CD10, which was absent in all the 20 control cases. Ultrastructural examination confirmed localization to the external surface of MVID cytoplasmic inclusions. Rab11 staining may be a useful adjunct in MVID diagnosis and the results support that myosin Vb dysfunction is important in the pathogenesis of MVID.