Focal segmental glomerulosclerosis (FSGS) is a rare form of kidney inflammation (glomerulonephritis) in which the glomeruli become increasingly scarred (sclerotic), leading to progressive loss of kidney function. Dysregulation of the immune system plays a role in pathogenesis, which is why immunosuppressive therapy with glucocorticoids can be successful, alongside supportive therapy (especially blocking of the renin-angiotensin system with ACE inhibitors or angiotensin receptor blockers). Many patients nevertheless require dialysis in the course of the disease. New therapeutic approaches that stabilize or protect kidney function are therefore needed.