Focal segmental glomerulosclerosis (FSGS) is a disease in which scar tissue develops on the glomeruli of the kidney. To allow for better understanding, it is best to breakdown these words: Focal : means that only some of the kidneys’ glomeruli have been damaged, while some are still normal. Glomerulo : A structure in the kidney. The glomeruli refers to the clusters of tiny blood vessels in the kidneys that filter waste and harmful substances from the blood. Each kidney has thousands of glomeruli. Sclerosis : refers to scarring. FSGS is most often idiopathic ( of unknown cause ), but can be caused by a variety of conditions such as the use of heroin or other drugs, HIV infection, obesity, sickle cell disease, atheroembolic disease, nephron loss, inherited genetic problems, and some medicines. Without treatment, primary FSGS may lead to kidney failure where the only treatment options are dialysis or kidney transplant. Glomerulosclerosis affects both children and adults. Males are affec...