Which of the following conditions is characterized by an deficiency of vitamin B12?

Pernicious anemia is characterized by a deficiency of vitamin B12 due to a lack of intrinsic factor, a protein necessary for the proper absorption of this vitamin in the intestines. Without sufficient vitamin B12, the body cannot produce enough healthy red blood cells, leading to anemia. This condition is specifically related to the body's inability to absorb the vitamin due to autoimmune damage to the gastric mucosa, which affects intrinsic factor production.

While B12 anemia might seem like a fitting answer, it is not a widely recognized term in clinical practice; rather, pernicious anemia specifically denotes the mechanism by which vitamin B12 deficiency arises because it entails the autoimmune aspect affecting absorption. Sickle cell anemia and hemolytic anemia are caused by different pathophysiological processes unrelated to vitamin B12 absorption or deficiency. Therefore, pernicious anemia is the correct condition associated with a deficiency of vitamin B12.