384
CASE FILES: BIOCHEMISTRY
A N SW E R S TO C A SE 42: C O B A L A M IN D E F IC IE N C Y
(V IT A M IN B 12)
Summary:
A 38-year-old vegetarian female with gradually worsening fatigue,
neurologic and GI symptoms, and megaloblastic anemia.
Diagnosis: Cobalamin (vitamin B12) deficiency.
Underlying problem: Lack of cobalamin intake with complete
vegetarian diet (vegan).
Causes of megaloblastic anemia: Folate and cobalamin deficiency.
Patients with folate deficiency have similar hematologic and GI findings
but do
not
have the neurologic symptoms as with cobalamin deficiency.
C L IN IC A L C O R R E L A T IO N
The two most common etiologies of megaloblastic anemia are deficiencies in
folate or cobalamin. Cobalamin deficiency can occur from a lack of intake
(such as with complete vegetarians), absence of intrinsic factor (either inher-
ited or from removal/damage to gastric mucosa), intestinal organisms, or ileal
abnormalities (tropical sprue). Patients present with anemic symptoms such as
fatigue, weakness, palpitations, vertigo, and tachycardia. GI symptoms include
sore, beefy-red tongue, weight loss, and diarrhea. Both folate and cobalamin
deficiencies have similar anemic and GI symptoms. However, cobalamin defi-
ciency also can present with numerous neurologic manifestations including:
numbness, parathesia, weakness, ataxia, abnormal reflexes, diminished vibra-
tory sensation, and disturbances in mentation (from irritability to psychosis).
Treatment consists of identifying/treating the underlying cause of deficiency
and replacement of cobalamin or folate.
O bjectives
1.
Describe the role of cobalamin in red blood cell formation.
2.
Explain why cobalamin deficiency leads to megaloblastic anemia.
3.
Develop a comprehension of the role of cobalamin in metabolism.
D efinitions
Cobalamin (vitamin B12) deficiency: Inadequate uptake of cobalamin
from the diet; often due to lack of intrinsic factor an intestinal transport
protein or less often due to unaugmented vegetarian diet that strictly
avoids meat or meat products, the source of dietary cobalamin.
Megaloblastic anemia: A disturbance in erythroid cell synthesis due to an
impaired DNA synthesis. This results in cells with small nuclei and nor-
mal cytoplasm, and a high RNA to DNA ratio. Impaired DNA synthesis
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