A Case of MIRAGE Syndrome with <i>SAMD9</i> Mutation and Refractory Infantile Diarrhea: Endoscopic Biopsy Evaluation via Light and Electron Microscopy

An infant with intrauterine growth restriction, suspected of having MIRAGE syndrome based on prenatal ultrasound, presented with genital ambiguity, adrenal insufficiency, intractable diarrhea from birth, and a pathogenic <i>SAMD9</i> mutation (<i>c.1376G>A, p.R459Q</i>). Endoscopic biopsies of the duodenum revealed complex light and electron microscopic abnormalities. Hypoplastic villi without signs of enteritis suggests a disorder of mucosal growth with reduced absorptive surface area contributes to intractable diarrhea. Ultrastructural study showed prominent dilated endoplasmic reticulum, abnormalities of Golgi morphology, specialized granule, and mucin processing. We hypothesize that the <i>SAMD9</i> mutation alters mucosal growth, and the processing of mucin, Paneth and neurosecretory granules, with premature degradation of specific granules in enterocyte lysosomes. These distinctive morphological findings support the idea that multisystem manifestations of MIRAGE syndrome are due to a primary disorder of microsomal trafficking.