Liver and Iron Metabolism - A Comprehensive Hypothesis for the Pathogenesis of Genetic Hemochromatosis

It is hypothesized that a homozygous C282Y mutation of the HFE gene prohibits the assembly of the transferrin-receptor 1 (TFR1) with the divalent metal transporter (DMT1) as the main iron update complex in hepatocytes membrane. Thus, the cellular influx of transferrin-bound iron from the endosomal compartment into the cytasol is compromised. As a consequence, transferrin saturation increases while concomitantly a cytosolic iron deficiency state develops. This in turn triggers the suppression of hepcidin synthesis in hepatocytes. Its impaired release into the bloodstream, causes the increased intestinal iron absorption of hemochromatosis. Excessively absorbed iron cannot be used by the erythron as a surplus for hemoglobin synthesis and is therefore trapped in ferritin complexes of RES macrophages. The ferritin is thereafter released into the bloodstream and taken up by hepatocytes for final disposal. In the lysosomal compartment ferritin is degraded to hemosiderin. Here, the release of excessive iron molecules may induce cellular injury via free radicals. The phenotypic expression of genetic hemochromatosis may depend on the activity of the erythron to use transferrin-bound-iron for heme synthesis. Therefore, a high erythron requirement for iron can utilize excess iron and may represent the rationale of phlebotomy therapy in this disease.

Megacolon and neurofibromatosis: a neuronal intestinal dysplasia. Case report and review of the literature

This study presents the case of a patient with neurofibromatosis and megacolon. A diffuse, but patchy abnormality of neural tissue was present throughout the colon, especially in the myenteric plexus, but also in the submucosal plexus, smooth muscles, and lamina propria. This consisted of (a) a marked decrease in the number of argyrophilic neurons within the myenteric plexus, enlargement and deformity of those neurons present, and a marked increase of nerve fibers and nerve tract size in the myenteric plexus; (b) a proliferation of neurons and nerve fibers within the smooth muscle and submucosa; and (c) a proliferation of nerve fibers within focal areas of the lamina propria. The relationship of this case to previously reported cases of neuronal intestinal dysplasia and plexiform neurofibromatosis is discussed. Surgical treatment may be necessary and the surgical options are reviewed.