Acquired Immunodeficiency Syndrome and the Nervous System

To the Editor.—  The workup described by Dalakas et al¹ for their patient with neuropathy and dementia was inadequate. B₁₂ deficiency is a significant cause of the neuropathy they describe in the absence of hematologic abnormalities and with normal B₁₂ levels.² In the fruit bat, the only animal model of B₁₂ deficiency, changes occur in fatty acid metabolism and plasma membranes.³Humans are the only animals that become B₁₂ deficient, resulting in hematologic effects.⁴ This could explain why animals do not develop acquired immunodeficiency syndrome even though the virus replicates in monkeys. B₁₂ is associated with impaired cellular immunity as evidenced by vegetarians, who have an increased incidence of tuberculosis.⁴ Cadmium, unlike lead and mercury, does not become methylated by B₁₂ but instead binds to the cobalt, destroying the function of the cofactor. The effects found in brain with