APOL1 and focal segmental glomerulosclerosis: To test the hypotheses that risk variant APOL1 is biochemically different in plasma and contributes to the development and progression of proteinuric kidney diseases like focal segmental glomerulosclerosis and arterionephrosclerosis, we developed assays to quantify APOL1 in plasma, to measure the size of APOL1-containing particles in plasma, and to quantify APOL1 in urine.