The APOL1 risk alleles, G1 and G2, are mutually exclusive (never occur on the same chromosome copy) and 2 copies are necessary to confer kidney disease risk (genotype may be G1/G1, G2/G2, or the compound heterozygous state of G1/G2). Variation in these alleles is now known to be responsible for the vast majority excess risk of non-diabetic kidney disease including FSGS, HIV-associated nephropathy, and unspecified CKD in African Americans.