The nature of the defects is not clear in these cases. Each of the above DNA synthetic abnormalities result in macrocytosis of erythrocytes. Although, not all macrocytosis is caused by abnormalities of DNA synthesis. The second most common cause of macrocytosis is abnormal DNA synthesis due to B12 or folate deficiency. Hypothyroidism, liver disease, and blood loss or hemolysis are also associated with macrocytosis.
Macrocytic anemia resulting from abnormal DNA synthesis is referred to as megaloblastic anemia.
Other endocrine disorders also cause anemia. The erythrocytes above are larger than the small lymphocyte, an indication of macrocytosis.