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Fat accumulation in enterocytes: a key to the diagnosis of abetalipoproteinemia or homozygous hypobetalipoproteinemia.

A 20-year-old woman was referred by her ophthalmologist to investigate the reason for her hypovitaminosis A and secondary night blindness. She had no other symptoms of deficiencies in fat-soluble vitamins, no abdominal complaints, and no weight loss. Laboratory examination revealed a deficiency in vitamin A (<12μg/dL, normal range 30–80) and vitamin E (<0.30mg/dL, normal range 0.5–1.8), a very low prothrombin time (30%), and very low levels of cholesterol (30mg/dL), triglycerides (4mg/dL), and LDL-cholesterol (below the level of detection). Her level of 25-hydroxy vitamin D appeared to be normal, but at the time of her first admission, vitamin D substitution had already been started. A slightly raised alanine aminotransferase was also detected (33U/L). Further work-up excluded cystic fibrosis, exocrine pancreas insufficiency, and celiac disease. Gastroscopy revealed a very pale duodenal mucosa; the villi, however, could be easily recognized (●" Fig.1). Videocapsule endoscopy revealed a pale small bowel mucosa with extremely pronounced villi (●" Fig.2,●" Video 1). Biopsies of the duodenal mucosa revealed areas of extended supranuclear vacuolization of the cytoplasm in the villi. These areas were interspersed with normal areas (●" Fig.3 and●" Fig.4). These findings suggested a diagnosis of either abetalipoproteinemia or homozygous hypolipobetaproteinemia, disorders that are caused by mutations in both alleles of the microsomal triglycerides transfer protein (MTP) or in the APO-B gene, respectively [1–2] This results in the failure of APO B-100 synthesis in the liver and APO B-48 synthesis in enterocytes, leading to fat accumulation in the small intestine. This diagnosis can be conFig.3 Microscopic image showing vacuolization, especially on the top of the villi. Vacuolization causes a paler aspect because of fat dissolving during the process of embedding the tissue in paraffin wax (“empty” vacuoles instead of fat accumulation).