Identification of a neutrophil-specific PIK3R1 mutation facilitates targeted treatment in a patient with Sweet syndrome

Acute febrile neutrophilic dermatosis (Sweet syndrome) is a potentially fatal multiorgan inflammatory disease characterized by fever, leukocytosis, and a rash with a neutrophilic infiltrate. Disease pathophysiology remains elusive, and current dogma suggests Sweet syndrome is a "reactive" process to an unknown antigen. Corticosteroids and steroid-sparing agents remain front-line therapies, but refractory cases pose a clinical challenge.A 51-year-old woman with multiorgan Sweet syndrome developed serious corticosteroid-related side effects and was refractory to steroid-sparing agents. Blood counts, liver enzymes, and skin histopathology supported the diagnosis. Whole genome sequencing, transcriptomic profiling, and cellular assays of patient's skin and neutrophils were performed.We identified elevated IL-1 signaling in lesional Sweet syndrome skin caused by a PIK3R1 gain-of-function mutation specifically found in neutrophils. This mutation increased neutrophil migration towards IL-1β and neutrophil respiratory burst. Targeted treatment with an IL-1R1 antagonist in the patient resulted in a dramatic therapeutic response and enabled tapering of corticosteroids.Dysregulated PI3K-AKT signaling is the first signaling pathway linked to Sweet syndrome and suggests Sweet syndrome may be caused by acquired mutations that modulate neutrophil function. Moreover, integration of molecular data across multiple levels identified a distinct subtype within a heterogenous disease that resulted in a rational and successful clinical intervention. Future cases will benefit from efforts to identify potential mutations. The ability to directly interrogate diseased skin allows this method to be generalizable to other inflammatory diseases and demonstrates a potential personalized medicine approach for challenging patients.FUNDING Berstein Foundation, NIH, VA, Moseley Foundation, and H.T. Leung Foundation.