Kidney biopsy specimens from patients diagnosed with lupus nephritis, IgA nephropathy, focal glomerular sclerosis, membranoproliferative glomerulonephritis, membranous glomerulonephropathy, and mesangial proliferative glomerulonephropathy displayed a significant reduction in SLC22A6 (OAT1) mRNA expression (and stable levels of SLC22A8, SLC22A7 and SLC22A11 expression). Here, SLC22A6 is linked to focal segmental glomerulosclerosis.