Erythrocytosis associated with IgA nephropathy

International audienceBackground Erythrocytosis is a hematological disorder usually related to hematopoietic stem cell somatic muta-tions. However, unexplained erythrocytosis remains frequent. In this study, we evaluated the involvement of IgA1, a regulator of erythropoiesis also implicated in IgA nephropathy (IgAN) pathophysiology, in unexplained polycythe-mia/erythrocytosis (PE) of IgAN patients.Methods IgAN-PE patients’ serum was collected, analyzed and used to study IgA1 effect on proliferation and differ-entiation of erythroid progenitors. Hematological parameters of transgenic mice for human alpha1 heavy chain were studied. Multicentric observational cohorts of chronic kidney disease (CKD) patients, including both native kidney diseases and renal transplants, were studied to analyze patient hemoglobin levels.Findings We retrospectively identified 6 patients with IgAN and unexplained PE. In large CKD cohorts, IgAN was associated with PE in 3.5% of patients (p