Pernicious Demyelination

Megaloblastic anaemia (pernicious anaemia), demyelinating neurological lesions in the spinal cord infertility. 

The story of vitamin B12 began with pernicious anemia, a disease that usually affects only persons of age 60 or more but which occasionally strikes children.3 Before 1926 the disease was incurable and usually fatal. Abnormally large, immature, and fragile red blood cells are produced but the total number of erythrocytes is much reduced from 4-6 x 106 mm-3 to 1- 3 x 106 mm-3. Within the bone marrow mitosis appears to be blocked and DNA synthesis is suppressed. The disease also affects other rapidly growing tissues such as the gastric mucous membranes (which stop secreting HC1) and nervous tissues. Demyelination of the central nervous system with loss of muscular coordination (ataxia) and psychotic symptoms is often observed. 

---