6. Relatives of patients with FSGS. In selected families (in which a patient has been found to have a mutation in an FSGS risk gene whose pathologic role has not been established), we will obtain individual histories of renal disease (hematuria, proteinuria, hypertension, nephrolithiasis) and will measure serum creatinine and urine protein excretion. We will include adults with and without renal disease and children with renal disease. We will evaluate children <18 years by obtaining a urine sample; if urinalysis and urine protein excretion are normal, we will not request a blood sample unless blood is being obtained for a clinical indication.