Atrophic gastritis is often a precursor to gastric cancer.Although the exact role of Helicobacter pylori infection in PA remains controversial, evidence indicates H. pylori is involved in the pathogenesis of the disease. A long-standing H. pylori infection may cause gastric autoimmunity by a mechanism known as molecular mimicry. Antibodies produced by the immune system can be cross-reactive and may bind to both H. pylori antigens and those found in the gastric mucosa. The antibodies are produced by activated B cells that recognise both pathogen and self-derived peptides. The autoantigens believed to cause the autoreactivity are the alpha and beta subunits of the sodium-potassium pump. In a study, B12 deficiency caused by Helicobacter pylori was positively correlated with CagA positivity and gastric inflammatory activity, rather than gastric atrophy. Less commonly, H. pylori and Zollinger-Ellison syndrome may cause a form of nonautoimmune gastritis that can lead to pernicious anemia.Impaired B12 absorption can also occur following gastric removal (gastrectomy) or gastric bypass surgery. In these surgeries, either the parts of the stomach that produce gastric secretions are removed or they are bypassed. This means intrinsic factor, as well as other factors required for B12 absorption, are not available. However, B12 deficiency after gastric surgery does not usually become a clinical issue. This is probably because the body stores many years worth of B12 in the liver and gastric surgery patients are adequately supplemented with the vitamin.Although no specific PA susceptibility genes have been identified, a genetic factor likely is involved in the disease.
Primary cutaneous histoplasmosis is a rare skin condition, reported on the penis, characterized by a chancre-type lesion with regional adenopathy. : 316

See also
Histoplasmosis


== References ==