Leukocytosis and a JAK2 mutation: The importance of expertise in somatic variant interpretation

This case details a patient presenting with a history of chronic leukocytosis with isolated eosinophilia, who was found to have a JAK2 G571S mutation by a next generation sequencing (NGS) panel for myeloproliferative neoplasm driver mutations. Adjunct NGS testing was performed on a sample of buccal cells to demonstrate this variant was a germline alteration, occurring in the absence of additional disease-causing mutations. The result caused the patient to be re-treated for a prior Strongyloides infection with ivermectin, which resolved his eosinophilia. This patient case highlights the likely benign polymorphic nature of the rare G571S JAK2 mutation that has been previously reported. Moreover, our results stress the importance of appropriate interpretation of rare variants of uncertain significance, namely that clinical decision making should be supported by adjunct genetic testing and with appropriate reference to each patient's clinical context.