A 6-month-old infant presents with hepatosplenomegaly, progressive neurodegeneration, and a cherry-red spot on fundoscopy. No features of bony involvement are present. Which enzyme is most likely deficient?
A) Alpha-galactosidase A
B) Glucocerebrosidase
C) Hexosaminidase A
D) Sphingomyelinase ✔
E) Sulphatase
Cherry-red spot + hepatosplenomegaly + neurodegeneration WITHOUT bone involvement = Niemann-Pick disease Type A (sphingomyelinase deficiency). Compare: Gaucher = hepatosplenomegaly + bone disease + NO cherry-red spot. Tay-Sachs = neurodegeneration + cherry-red spot + NO hepatosplenomegaly. Fabry = X-linked, pain + skin + kidney, no cherry-red spot. The combination of hepatosplenomegaly AND cherry-red spot narrows to Niemann-Pick.
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Haemolysis caused by poisonous snake bite may be due to formation of which of the following?
A) Cardiolipin
B) Cephalin
C) Lysolecithin ✔
D) Phosphatidic acid
E) Sphingomyelin
SNAKE VENOM contains PHOSPHOLIPASE A2 → cleaves the FATTY ACID at C2 of PHOSPHATIDYLCHOLINE (lecithin) → LYSOLECITHIN (lyso-phosphatidylcholine) + free fatty acid. LYSOLECITHIN is a DETERGENT-LIKE molecule → inserts into RBC membrane → disrupts membrane integrity → HAEMOLYSIS. Also: phospholipase A2 cleaves phospholipids in tissue cell membranes → releases arachidonic acid → eicosanoid synthesis → inflammation. Phospholipase A2 also releases the substrate for platelet activating factor synthesis.
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Sphingomyelins on hydrolysis yield which of the following?
A) Glycerol, fatty acid, phosphoric acid, choline
B) Glycerol, sphingosine, fatty acid, choline
C) Sphingosine, fatty acid, phosphoric acid, choline ✔
D) Sphingosine, phosphoric acid, glycerol, inositol
E) Sphingosine, phosphoric acid, glycerol, serine
SPHINGOMYELIN = ceramide + phosphocholine. HYDROLYSIS by sphingomyelinase → SPHINGOSINE + FATTY ACID + PHOSPHORIC ACID + CHOLINE. Key: sphingomyelin has NO glycerol (unlike glycerophospholipids). The backbone is SPHINGOSINE (amino alcohol). Compare: lecithin (phosphatidylcholine) hydrolysis → glycerol + 2 fatty acids + phosphoric acid + choline. The presence of SPHINGOSINE (not glycerol) distinguishes sphingomyelin hydrolysis products from glycerophospholipid hydrolysis.
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425 MCQs are arranged to the learning outcomes of this uhs.