Biochemistry Dennis is a 63 year old man who has been suffering from dementia. H
ID: 217976 • Letter: B
Question
Biochemistry
Dennis is a 63 year old man who has been suffering from dementia. He has been a long-term vegan, and recently began having mood swings and depression. On testing his blood work, there is evidence of anemia and low vitamin B12. His serum homocysteine level was 65.34 ?mol/L (normal range, 4.60–12.44). His doctor initiated weekly injectable vitamin B12 and 5 mg of folic acid daily. He has had a remarkable improvement in mood and his mental state has also improved. Without diet change, his serum homocysteine level was normalized to 8.32 ?mol/L (normal range, 4.60–12.44).
Based on the symptoms presented, and response to treatment, which enzymes/vitamins appear to be deficient or not functioning properly? What type of homocystinuria does Dennis have? Why was the treatment successful? Explain your reasoning.
Explanation / Answer
Homocystinuria is an autosomal recessive inherited defect of the methionine or transsulfuration pathway resulting in abnormal accumulation of homocystein and its metabolites.
The accumulation of homocysteine and its metabolites are caused by the disruption of any of the three pathways of methionine metabolism. Deficiency in enzyme cystathionine B-synthase, defective methylcobalamin synthesis and abnormality in methylene tetrahydrofolate reductase can result in this accumulation. Clinically the abnormalities resulting from any of the above abnormalities is termed as homocystinuria I, II and III.
From the symptoms that Dennis shows, he seems to be suffering from homocystinuria III.
The gene cystathionine beta-synthase [ CBS] gene holds instructions for making an enzyme that uses vitamin B6 to metabolise the amino acid homocysteine and serine. Mutation in this gene disrupts this activity.
The amino acid homocysteine is obtained from meat . A high level of homocystein in the blood is associated with low levels of vitamins B6 , B12 and folate.
Since, Dennis is a vegan, his diet is devoid of meat , eggs or any other animal product. So the homocysteine level was immediately brought under control by administering him with vit B12.
Folate is found in natural food products but folic acid is a synthetic form of vitamin B9. It is essential for proper functioning of the brain , for producing new cells and to prevent certain types of anemia. So , dose of folic acid helped Dennis to overcome his mood swings and improved his mental state. Since all the B vitamins are water soluble, the body cannot store them . This is why external supplements are important if the body is not getting enough of it from food.
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