Homocystinuria due to cystathionine beta-synthase (CBS) deficiency causes thromboembolism. Which mechanism explains the prothrombotic state?

• A Elevated S-adenosylmethionine inhibits platelet aggregation
• B Accumulation of methionine directly activates the intrinsic coagulation cascade
• C Deficient cystathionine impairs antithrombin III synthesis
• D Homocysteine causes endothelial oxidative damage and upregulates tissue factor expression ✓

Explanation

Homocysteine promotes thrombosis through endothelial injury, oxidative stress, upregulation of tissue factor, and impaired nitric oxide availability. Homocysteinylation of proteins disrupts vascular homeostasis. Methionine accumulation does not directly activate coagulation. CBS deficiency causes homocystinuria with homocysteine and methionine elevation, and cystathionine is low.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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