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Microvillus Inclusion Disease- A Deadly Masquerader Christine Beeson BA OMSIII, Jeffrey C. Weiss MD, Robert D. Ligorsky DO MACOI FACP FAHA Objective: Case Description: Discussion: To raise awareness of this disorder so that recognition of this deadly disease can be made early, and to further research in an attempt to find a cure. A Navajo female infant presented to Phoenix Children’s Hospital on day 6 of life with watery diarrhea. Pregnancy and delivery were unremarkable. Family history was noncontributory for metabolic or gastrointestinal disorders. Physical exam revealed a markedly dehydrated infant in apparent distress with massive liquid, almost urine-like stools. Stool volume quantification found large losses ranging from 100-500 mL/kg/day. She was found to have developed metabolic acidosis. The diarrhea persisted despite complete bowel rest. The stool electrolytes were high in Na and low in K, consistent with a secretory diarrhea. TPN and intravenous fluids were administered, but the stool volume still remained high. Several tests were done to detect a gamut of metabolic, infectious, immunologic, and hormonal causes of diarrhea, all of which were unremarkable. A small bowel biopsy revealed features consistent with MVID. This case of MVID illustrates the value of rapid diagnosis and treatment. There is increased prevalence of MVID in groups with consanguineous parents. Populations in England, the Middle East, and in the Navajo Indians have an increased incidence of this rare disease. The differential diagnosis includes chloridelosing diarrhea, enzyme/micronutrient deficiencies, congenital short bowel, tufting disease, and defective sodium-hydrogen exchange. Clinical diagnosis is made by duodenal biopsies demonstrating complete villous atrophy, vacuolated cytoplasm, and alkaline phosphatase-positive inclusions in the apical cytoplasm. Light microscopy demonstrates abnormal PASpositive material in the apical cytoplasm, and electron microscopy illustrates microvillus inclusions and an absent brush border. Intestinal failure and associated diarrhea cannot be cured and infants are totally dependent on parenteral nutrition. Metabolic decompensation, dehydration, recurrent infections, and complications involving the liver and kidneys make long-term outcomes poor. These patients are candidates for small bowel transplantation and should be managed in centers that are equipped to perform the necessary procedures. Introduction: Microvillus Inclusion Disease (MVID) is a rare autosomal recessive disorder that was first described by Davidson in 1978. Mutations in the MYO5B gene located on chromosome 18 have been found in most patients resulting in loss of function of the myosin Vb5protein. As a result intestinal microvilli cannot be properly formed. The disorder most often presents as life-threatening diarrhea in newborns, leading to massive dehydration and electrolyte imbalance. Total parenteral nutrition (TPN) is required to maintain life until a small bowel transplant can be performed. In some patients lifelong nutritional support is necessary. Complications of parenteral nutrition can have a major impact on survival. Normally, vesicles from the Golgi (Go) carry brush border components to the cell surface for assembly (open arrow). This path may be blocked in MVID, leading to retention of vesicles (VB), giving rise to microvillus inclusions (MI). Nu=nucleus, Ly=lysosome References: 1. Cutz E, Sherman PM, Davidson GP. Enteropathies associated with protracted diarrhea of infancy: clinicopathological features, cellular and molecular mechanisms. Pediatric Pathology & Laboratory Medicine May-June 1997;17(3):335-67. 2. Erickson RP, Larson-Thomé K, Valenzuela RK, Whitaker SE, Shub MD. Navajo microvillous inclusion disease is due to a mutation in MYO5B. American Journal Medical Genetics A. 2008;146A: 3117–3119. 3. Ruemmele F, Schmitz J, Goulet O. Microvillous inclusion disease (microvillous atrophy). Orphanet Journal Of Rare Diseases. January 2006;1:22-5. Transmission electron micrograph of surface enterocyte showing microvillus inclusions (MI) with inwardly facing brush border microvilli (arrow). Acknowledgements: Thank you to Dr. Chris Spiekerman, Dr. Robert Ligorsky, and Dr. Jeffrey Weiss for the production, support, and revision of this poster presentation.