Functional vitamin B12 deficiency

Pract Neurol. 2009 Feb;9(1):37-41. doi: 10.1136/jnnp.2008.161968.


We describe a case of functional vitamin B12 deficiency where the repeated measurement of a serum B12 level within the normal range led to delay in the diagnosis of subacute combined degeneration of the spinal cord, and possibly permanent neurological damage as a result. Failure of intracellular transport of B12 by transcobalamin-2 can lead to functional B12 deficiency but with apparently normal serum levels, and is suggested by raised levels of either serum methylmalonic acid or homocysteine, associated with low levels of transcobalamin-2. Such patients may respond to repeated high-dose injections of B12.

Publication types

  • Case Reports
  • Historical Article

MeSH terms

  • Aged
  • Female
  • History, 19th Century
  • History, 20th Century
  • Humans
  • Magnetic Resonance Imaging / methods
  • Portraits as Topic
  • Vitamin B 12 / chemistry
  • Vitamin B 12 Deficiency / history
  • Vitamin B 12 Deficiency / pathology
  • Vitamin B 12 Deficiency / physiopathology*


  • Vitamin B 12