Pernicious anemia is a decrease in red blood cells that occurs when the body cannot properly absorb vitamin B12 from the gastrointestinal tract. Vitamin B12 is necessary for the proper development of red blood cells.

Pernicious anemia is a type of megaloblastic anemia.

See also: Anemia

The body needs vitamin B12 to make red blood cells. To provide vitamin B12 to your blood cells, you need to eat enough foods containing vitamin B12, such as meat, poultry, shellfish, eggs, and dairy products.

To absorb vitamin B12, your body uses a special protein called intrinsic factor, which is released by cells in the stomach. The combination of vitamin B12 bound to intrinsic factor is absorbed in the last part of the small intestine.

When the stomach does not make enough intrinsic factor, the intestine cannot properly absorb vitamin B12.

Very rarely, infants and children are born without the ability to produce enough intrinsic factor, or the ability to absorb the combination of intrinsic factor and vitamin B12 in the small intestine. Pernicious anemia that occurs at birth (congenital) is inherited. You need the defective gene from each parent to get it.

Common causes of pernicious anemia include:

• Weakened stomach lining (atrophic gastritis)
• The body's immune system attacking the cells that make intrinsic factor (autoimmunity against gastric parietal cells) or intrinsic factor itself

The disease begins slowly and may take decades to fully establish. Although the congenital form occurs in children, pernicious anemia usually does not appear before age 30 in adults. The average age at diagnosis is 60.

Risk factors include:

• Family history of the disease
• History of autoimmune endocrine disorders, including:
  • Addison's disease
  • Chronic thyroiditis
  • Graves disease
  • Hypoparathyroidism
  • Hypopituitarism
  • Myasthenia gravis
  • Secondary amenorrhea
  • Type 1 diabetes
  • Testicular dysfunction
  • Vitiligo
• Scandinavian or Northern European descent

See also: Anemia - B12 deficiency for other causes of low vitamin B12 levels.