“Why does B12 deficiency cause neuropathy but B9 deficiency does not?”

Added: 2026-05-05

[00:00:00]Why does B12 deficiency cause neuropathy, but B9 deficiency does not?

[00:00:04]Okay. Well, as you guys know, both B9 and B12 are required for DNA synthesis.

[00:00:09]So, if the bone marrow can't produce RBC's and neutrfils as readily as it's supposed to, then you can get abnormalities. The size of the RBC increases and the number of loes of the nucleus within the neutrfll will increase. Student is asking about the neuropathy for B12 deficiency. However, easy answer. Now when we talk about the fancy biochemistry, you have one reaction where you have the conversion of methyl malanial coa into suinal coa and B12 is needed for that conversion.

[00:00:42]It's a co-actor for a methylmelanal coa mutase. So if we have B12 deficiency, we get a buildup of methylonic acid aka methylmelanil coa for all intents and purposes and that's toxic to myelin.

[00:00:55]So that's not related to B9.

[00:00:58]If you have deficiency of B9, you can still carry out that reaction. You don't get a buildup of methan malanil coa. So points on us, not only knowing that, but this is what I want you to memorize. If you have B12 deficiency, you're going to have a buildup of methylanal coa. It's an up arrow for methylanal coa or methylonic acid. No change for B9 deficiency for methylanal coa. Methylammonic acid in both B9 and B12 deficiencies we get increased homoysteine more fancy biochemistry stuff just memorize it okay so up arrow homoysteine for both B9 B12 deficiencies only an up arrow for methylmelanal coa for B12 deficiency not for B9 deficiency