Abstract
Ezrin, encoded by EZR, is a central module of epithelial polarity and links membrane proteins to the actin cytoskeleton directly or indirectly through scaffold proteins in the epithelium. Ezrin knockout mice fail to thrive and do not survive past weaning. We identified a homozygous EZR loss-of-function (LoF) variant, c.356dup, by exome sequencing in an infant with intractable diarrhea and failure to thrive, who died from septicemia at 5 months of age. The variant localized within a homozygous region of 13.2 Mb in the proband, is consistent with inheritance identical-by-descent from the consanguineous parents, and segregated with disease in the proband's family. EZR transcript analyses in a heterozygous carrier showed that the variant triggers nonsense-mediated mRNA decay. Homozygous EZR LoF variants have not been reported in public databases. In this study, we generated a Caco-2 EZR knockout cell line to investigate the role of ezrin in human intestinal epithelia. Our analyses used electron and immunofluorescence microscopy to assess structural changes in the knockout cells. We observed significant disorganization of the terminal web region, microvillus rarefaction and abnormal branching. Furthermore, the absence of ezrin resulted in the mislocalization of the ezrin-interacting scaffold protein Na+/H + exchanger regulatory factor-1. In conclusion, this represents the first documentation of complete ezrin deficiency in humans, highlighting the essential and non-redundant functions of the protein in maintaining intestinal physiology.