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Byte+: ET: Genetics & Phenotype Correlations
A 32-year-old male presents with a markedly elevated platelet count of 1,200 x 10^9/L during a workup for fatigue. Initial molecular testing is negative for the JAK2 V617F mutation. The team suspects a specific alternative driver mutation given the patient's young age, male sex, and extreme thrombocytosis
High Yield Points:
-90% of ET cases have mutually exclusive driver mutations.
-Order of frequency: JAK2 (60%) > CALR (20-25%) > MPL (5%).
-Triple-negative ET (10-15%) --> exclusion of reactive causes is vital.
-CALR mutations associated with younger age and male sex.
-CALR phenotype: Higher platelet counts, lower hemoglobin than JAK2.
-CALR patients have lower thrombosis risk than JAK2-mutated patients.
-JAK2 V617F associated with higher hemoglobin/WBC and thrombosis risk.
Additional Concepts:
-MPL mutations (5%) have no specific prognostic significance regarding thrombosis/survival.
-Triple negative cases may harbor noncanonical mutations (e.g., TET2, ASXL1).
-Presence of mutation distinguishes clonal thrombocytosis from reactive.
-Mutation type does NOT differentiate ET from PV or PMF alone.
Mutation | Frequency | Clinical Phenotype Associations |
|---|---|---|
JAK2 V617F | 60-65% | Older age, higher Hgb/WBC, increased thrombosis risk |
CALR | 20-25% | Younger age, male, extreme thrombocytosis, lower thrombosis risk |
MPL | ~5% | Similar to general ET, no unique prognostic features |
Triple Negative | 10-15% | Diagnosis of exclusion; ensure not reactive |
Key insights: Genetic profiling in ET is essential not only for diagnosis but for anticipating clinical phenotype; JAK2 mutations correlate with higher thrombotic risk and older age, whereas CALR mutations are associated with younger patients and more extreme thrombocytosis. Approximately 10-15% of patients are triple negative, requiring rigorous exclusion of reactive causes and other myeloid neoplasms.
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Ranjan Pathak
Founder, ReviewBytes