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Delayed-onset muscle soreness — MRCP Part 1 MCQ

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HardExercise PhysiologyDelayed-onset muscle sorenessMRCP Part 1

A woman has lifelong mucocutaneous and surgical bleeding. Platelet count, morphology, von Willebrand studies and glycoprotein IIb/IIIa expression are normal. Aggregation is impaired to several agonists, while high-dose agonists produce delayed residual aggregation. Which defect best fits?

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Correct answer: C — CalDAG-GEFI deficiency

The best answer is “CalDAG-GEFI deficiency”. Biallelic RASGRP2 variants cause CalDAG-GEFI deficiency. CalDAG-GEFI rapidly activates Rap1 and thereby alpha-IIb-beta-3 integrin; deficient platelets show impaired aggregation to multiple agonists despite normal integrin expression, with slower alternative signalling sometimes allowing residual responses at high agonist concentrations. Kindlin-3 deficiency causes leukocyte adhesion deficiency type III, while glycoprotein Ib and dense-granule disorders have different phenotypic or laboratory signatures.

Reference: Expanded repertoire of RASGRP2 variants responsible for platelet dysfunction and severe bleeding: https://pmc.ncbi.nlm.nih.gov/articles/PMC5785798/