Unequal Effects of Myosin 5B Mutations in Liver and Intestine Determine the Clinical Presentation of Low-Gamma-Glutamyltransferase Cholestasis

Mutations in the MYO5B gene cause in some patients low gamma-glutamyltransferase (low-GGT) cholestatic liver disease (CLD) and in other patients microvillus inclusion disease (MVID, a congenital diarrheal and malabsorption disorder). Overlap of symptoms occurs but more MVID patients present cholestasis than CLD patients present diarrhea. Clinical observations indicate that MYO5B mutations can cause but also protect against CLD. This complicates family counseling and therapeutic decisions. Here we have reviewed the literature on MYO5B mutations in relation to CLD. It appears that variations in the clinical presentation of low-GGT CLD can be attributed to the coincident expression but unequal effects of MYO5B mutations in hepatocytes versus enterocytes, two cell types that jointly constitute the core of the enterohepatic circulation. Therefore, contrasting other low-GGT CLDs, those associated with MYO5B mutations should be viewed as a disease of the enterohepatic circulation rather than solely of the liver.