Benign familial hematuria, also known as thin-basement-membrane nephropathy, is a kidney disease that usually begins during childhood. The disorder is characterized by the presence of red blood cells in the urine (hematuria). The blood in the urine may be present in microscopic amounts (microscopic hematuria) and not visible to the eye, present in small amounts that give the urine a "cloudy" or "smoky" appearance, or easily visible. Many individuals with the disorder have abnormalities of the kidney's glomeruli, the clusters of small blood vessels (capillaries) that normally filter the blood passing through the kidneys (glomeruli filtration). In such cases, the membrane (basement membrane) supporting the loops of capillaries that make up the renal glomeruli may be abnormally thin. Benign familial hematuria may be inherited as an autosomal dominant genetic trait.