sing
Forum Guru
Topics: 153
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A patient has been weak and falling down frequently. He is suspicious and irritable. His skin is pale, his tarsal plates are pale, and he has a loss of vibration sense over his legs and trunk. His legs show a symmetric weakness with decreased deep tendon reflexes. The leading theory for the pathophysiology of this disorder relates to which of the following?
A. Anamolous insertion of even-chain fatty acids into membrane lipids
B. Anomalous insertion of odd-chain fatty acids into membrane lipids
C. Increased vitamin A intake
D. Lack of methylmalonyl CoA
E. Lack of propionyl CoA
A&Y
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| MLF
Forum Elite
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This is vit B12 neuropathy, the answer should be B
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| Kazem
Forum Elite
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Agree with MLF, Answer is B.
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| sing
Forum Guru
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but why vit b12 deficiency will cause anomalous insertion of odd-chain fatty acids into membrane lipids? could you explain?
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| Malaysian
Forum Guru
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its because Vit.B12 is a co-factor of an enzyme(I forgot the name but it has malonoyl in its name!!)which helps break down the odd chain fatty acid.So lack of vit. B12 leads to build up of odd chain fatty acid and since myelin sheaths of Peripheral nerves are basically lipid compounds so abnormal myelination.
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| sing
Forum Guru
Topics: 153
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sounds really make sense. thanks a lot.
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| MLF
Forum Elite
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Basically what malaysian said, but i'll just say it in diffferent words:
Normally odd chain and even chain fatty acids, when go thru beta oxidation, both produce acetyl coA, but odd chain yields 2 acetly co A whereas even chain gives one acetyl coA and one propiniolcoA. This propionyl coA needs to be broken down further and its made into methylmalonly coA which in turn is converted to succinly coA , and can contribute to glucose thru TCA cycle. Now the methylmalonly CoA reaction towards Succinly coA is by the enzyme methylmalonly CoA mutase, which requires Vit B12 as a cofactor, without which, it builds up and also propionyl coA can't be broken down which is toxic to myelin hence resulting in vit B12 neuropathy. So the whole path depends on ODD CHAIN fatty acid pathway. Hope I cleared it further.
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| docofthebigapple
Forum Senior
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Hi I'd just want to quickly add something here.
Its the Beta oxidation of even carbon numbered saturated fatty acids that yields Acetyl CoA {2 carbon} in the end. And the Odd Carbon numbered fatty acids end up in propionyl CoA {3 carbon}, which enters the Citric Acid Cycle as described by MLF.
Vitamin B-12 is a co-factor of the enzyme methyl malonyl CoA mutase that converts methylmalonyl CoA into Succinyl CoA. Conversion of Propionyl CoA into methyl malonul CoA however requires Biotin.
Thanks.
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| olive
Forum Newbie
Topics: 4
Posts: 17
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The vitamin B12 Coenzyme in this pathway (Odd number Fatty Acid) is Methylmalonyl CoA Mutase.
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