Autoimmune atrophic gastritis is a chronic inflammatory disease in which the immune system mistakenly destroys a special type of cell (parietal cells) in the stomach. Parietal cells make stomach acid (gastric acid) and a substance our body needs to help absorb vitamin B12 (called intrinsic factor). The progressive loss of parietal cells may lead to iron deficiency and finally vitamin B12 deficiency. The clinical signs and symptoms of iron deficiency anemia include tiredness, pale complexion, and heart problems such as exercise intolerance and palpitations. B12 deficiency may lead to pernicious anemia as well as gastrointestinal and neurological problems. Autoimmune atrophic gastritis may also be associated with an increased risk of certain types of stomach cancers.

The cause of autoimmune gastritis is unknown, but affected people are likely to have other autoimmune disorders including autoimmune thyroiditis, diabetes type I, Addison’s disease, and vitiligo. Diagnosis is made through a combination of clinical findings (certain blood tests and presence of other autoimmune conditions) and biopsy of stomach lining. Treatment is based on the signs and symptoms present in each person, but may include iron infusions, vitamin B12 injections and endoscopic surveillance.

Autoimmune atrophic gastritis is considered a "precancerous" condition and it may be responsible for the development of gastric adenocarcinoma or carcinoids.

Autoimmune atrophic gastritis is considered an autoimmune disorder. In people who are affected by this condition, the immune system mistakenly attacks the healthy cells of the stomach lining. Overtime, this can wear away the stomach's protective barrier and interfere with the absorption of several key vitamins (i.e. vitamin B12, iron, folate). This leads to the signs and symptoms of autoimmune atrophic gastritis.

In autosomal dominant conditions, an affected person only needs a change (mutation) in one copy of the responsible gene in each cell. In some cases, an affected person inherits the mutation from an affected parent. Other cases may result from new (de novo) mutations in the gene. These cases occur in people with no history of the disorder in their family. A person with the condition has a 50% chance with each pregnancy of passing along the altered gene to his or her child.

In some cases, periodic endoscopy may also be recommended due to the increased risk of certain types of cancer.

The long-term outlook (prognosis) for people with autoimmune atrophic gastritis varies. The condition is associated with an increased risk of pernicious anemia, gastric polyps and gastric adenocarcinoma. Significant risk factors for the development of gastric cancer in autoimmune atrophic gastritis include pernicious anemia, severity of atrophy, intestinal metaplasia, length of disease duration, and age older than 50 years. Fortunately, early diagnosis and proper treatment can reduce the mortality of the condition.