Leukemia-predisposing conditions, such as GATA2 haploinsufficiency, are known for their high penetrance and expressivity profiles. These disorders pose a difficult diagnostic challenge to even the most experienced clinician when they first present. We describe the case of a 17-year-old male presenting with features of nontuberculous mycobacterial infection, pulmonary fibrinoid granulomatous vasculitis, and myelodysplasia in the setting of a pathogenic GATA2 frameshift mutation confirmed by next-generation sequencing. The broad differential for GATA2 haploinsufficiency requires prompt recognition of key clinical features and laboratory abnormalities towards directing diagnosis and guiding appropriate and perhaps life-saving therapy.