Case Study: You have a 20-year-old patient who was normal at birth but soon disp

Question

Case Study: You have a 20-year-old patient who was normal at birth but soon displayed delayed development of intellect and motor skills. He has high levels of sialic acid in his urine and his blood You culture his fibroblasts. What are fibroblasts and why does it make sense to culture them? The cultured cells have a high intracellular level of sialic acid and surprisingly high amounts of sialic acid in the lysosomes What happens in lysosomes? You do an experiment in which you add a radioactive sialic acid derivative to a sample of his lysosomes and to those of a normal person. Compared with a normal person, your patient's degraded sialic acid leaves the lysosome very slowly. What does this tell you? d. You measure the intracellular activities of N-acetylneuraminate lyase, sialidase, CMP-N-acylneuraminate phosphodiesterase, and acylneuraminate citidytyl transferase and find that they are normal. Are these all or mostly degrading or synthesizing enzymes? e. Is the defect in your patient more likely to be in the sialic acid synthesis pathway or in the pathway for degrading it? Justify your choice.

Explanation / Answer

** It would have been better if you mentioned the exact concentration of sialic acid in blood.

a) Fibroblasts are cells found in connective tissue. They are responsible for the formation of collagen and other fibres. This patient is having abnormally high level of sialic acid in his blood. Fibroblast cells having abnormal amount of sialic acid are suspected to be suffering from Salla's disease.

b) Sialin is a lysosomal membrane protein which transports sialic acid out from lysosomes. Patients suffering from Salla's disease are lack this protein Sialin. So, sialic acid remains in lysosomes. This is a autosomal recessive disorder.

c) As I have already mentioned in a and b, Sialic acid is not been removed and is being accumulated in the lysosomes. This is due to deficiency of sialin. The sialin protein is coded by the gene SLC17A5 located on chromosome no.6.

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