Alzheimer's disease: a 'cobalaminergic' hypothesis.

An association between Alzheimer's Disease (AD) and low CSF and serum vitamin B12 (B12) has recently been described (1, 2, 3). This is apparently independent of nutritional intake (4). It has been suggested that such patients may exhibit an atypical form of cobalamin deficiency (3, 4). It is therefore proposed that these deficiencies may be aetiologically important, at least in sub-groups of AD, and a mechanism is described whereby B12 deficiency may result in the characteristic neurotransmitter changes of the disease. The hypothesis generates predictions regarding biochemical evaluation of such patients and suggests associations between the neurochemical disturbances and structural abnormalities of AD.