Master Vitamin B12 (Cobalamin) Mechanism and Deficiency with Picmonic for Physician Assistant

Vitamin B12 is also called cobalamin, which is derived from English terms to mean “cobalt vitamin”.

Vitamin B12 is found in foods that come from animals and is stored largely in the liver, where it creates a substantial reserve for extended periods without animal-based foods.

Methionine synthase is a vitamin B12-dependent enzyme. This enzyme converts homocysteine to methionine, which plays a key role in DNA synthesis.

Methylmalonyl Coenzyme A mutase is a vitamin B12-dependent enzyme. This enzyme converts methylmalonyl CoA to succinyl CoA.

Because vitamin B12 plays an essential role in DNA synthesis, a vitamin B12 deficiency can cause abnormalities in blood cells, which have rapid turnover and are significantly affected by poor DNA synthesis. Therefore, a vitamin B12 deficiency can manifest as a macrocytic, megaloblastic anemia, indicating immature red blood cells.

Because vitamin B12 plays an essential role in DNA synthesis, a vitamin B12 deficiency can cause abnormalities in blood cells, which have rapid turnover and are significantly affected by poor DNA synthesis. Therefore, a vitamin B12 deficiency can manifest as hypersegmented neutrophils, indicating immature neutrophils.

A vitamin B12 deficiency can be distinguished from a folate deficiency by the presence of neurologic symptoms resulting from damage to the spinal cord.

The posterior column is the white matter tract in the dorsomedial side of the spinal cord. This tract contains ascending fibers important for fine touch, vibration, pressure, and proprioception. This tract is commonly affected in vitamin B12 deficiency due to demyelination caused by buildup of methylmalonic acid.

This tract begins in the motor area of the cerebral hemisphere on the contralateral side, decussates in the medulla and descends to the anterior horn of the spinal cord in the lateral corticospinal tract. This tract controls movement of ipsilateral limbs. This tract is commonly affected in vitamin B12 deficiency due to demyelination caused by buildup methylmalonic acid.

This is a set of fibers that begins in the spinal cord and terminates in the ipsilateral cerebellum where it conveys information about limb and joint position. This tract is especially important for fine movement and damage to this tract can cause ataxia. This tract is commonly affected in vitamin B12 deficiency due to demyelination caused by buildup of methylmalonic acid.