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Decreased Brain Levels of Vitamin B12 in Aging, Autism and Schizophrenia.

Zhang Y, Hodgson NW, Trivedi MS, Abdolmaleky HM, Fournier M, Cuenod M, Do KQ, Deth RC. (2016) PLoS One. 11(1) e0146797. doi: 10.1371/journal.pone.0146797. eCollection 2016. 

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Abstract:



Many studies indicate a crucial role for the 
vitamin B12 and folate-dependent enzyme methionine synthase (MS) in brain development and function, but vitamin B12 status in the brain across the lifespan has not been previously investigated. 

Vitamin B12 (cobalamin, Cbl) exists in multiple forms, including methylcobalamin (MeCbl) and adenosylcobalamin (AdoCbl), serving as cofactors for MS and methylmalonylCoA mutase, respectively.

We measured 
levels of five Cbl species in postmortem human frontal cortex of 43 control subjects, from 19 weeks of fetal development through 80 years of age, and 12 autistic and 9 schizophrenic subjects.

Total Cbl was significantly lower in older control subjects (> 60 yrs of age), primarily reflecting a >10-fold age-dependent decline in the level of MeCbl. 
Levels of inactive cyanocobalamin (CNCbl) were remarkably higher in fetal brain samples.

In both autistic and schizophrenic subjects MeCbl and AdoCbl 
levels were more than 3-fold lower than age-matched controls.

In autistic subjects lower MeCbl was associated with 
decreased MS activity and elevated levels of its substrate homocysteine (HCY). Low levels of the antioxidant glutathione (GSH) have been linked to both autism and schizophrenia, and both total Cbl and MeCbl levels were decreased in glutamate-cysteine ligase modulatory subunit knockout (GCLM-KO) mice, which exhibit low GSH levels.

Thus our findings reveal a previously unrecognized decrease in 
brain vitamin B12 status across the lifespan that may reflect an adaptation to increasing antioxidant demand, while accelerated deficits due to GSH deficiency may contribute to neurodevelopmental and neuropsychiatric disorders.