Trypanolytic variants in APOL1, which encodes apolipoprotein L1, associate with kidney disease in African Americans, but whether APOL1-associated glomerular disease has a distinct clinical phenotype is unknown. Here we determined APOL1 genotypes for 271 African American cases, 168 European American cases, and 939 control subjects. In a recessive model, APOL1 variants conferred seventeenfold higher odds (95% CI 11 to 26) for focal segmental glomerulosclerosis (FSGS) and twenty-ninefold higher odds (95% CI 13 to 68) for HIV-associated nephropathy (HIVAN). FSGS associated with two APOL1 risk alleles associated with earlier age of onset (P ϭ 0.01) and faster progression to ESRD (P Ͻ 0.01) but similar sensitivity to steroids compared with other subjects. Individuals with two APOL1 risk alleles have an estimated 4% lifetime risk for developing FSGS, and untreated HIVinfected individuals have a 50% risk for developing HIVAN. The effect of carrying two APOL1 risk alleles explains 18% of FSGS and 35% of HIVAN; alternatively, eliminating this effect would reduce FSGS and HIVAN by 67%. A survey of world populations indicated that the APOL1 kidney risk alleles are present only on African chromosomes. In summary, African Americans carrying two APOL1 risk alleles have a greatly increased risk for glomerular disease, and APOL1-associated FSGS occurs earlier and progresses to ESRD more rapidly. These data add to the evidence base required to determine whether genetic testing for APOL1 has a use in clinical practice.

The increased burden of chronic kidney and end-stage kidney diseases (ESKD) in populations of African ancestry has been largely unexplained. To identify genetic variants predisposing to idiopathic and HIV-1-associated focal segmental glomerulosclerosis (FSGS), we carried out an admixture-mapping linkage-disequilibrium genome scan on 190 African American individuals with FSGS and 222 controls. We identified a chromosome 22 region with a genome-wide logarithm of the odds (lod) score of 9.2 and a peak lod of 12.4 centered on MYH9, a functional candidate gene expressed in kidney podocytes. Multiple MYH9 SNPs and haplotypes were recessively associated with FSGS, most strongly a haplotype spanning exons 14 through 23 (OR = 5.0, 95% CI = 3.5-7.1; P = 4 × 10 −23 , n = 852). This association extended to hypertensive ESKD (OR = 2.2, 95% CI = 1.5-3.4; n = 433), but not type 2 diabetic ESKD (n = 476). Genetic variation at the MYH9 locus substantially explains the increased burden of FSGS and hypertensive ESKD among African Americans.The prevalence of chronic kidney disease (CKD) in the United States is currently estimated at 13% and is associated with significant morbidity and mortality 1 . Approximately 100,000 Americans develop end-stage kidney (renal) disease (ESKD) each year. The cumulative lifetime risk for ESKD varies by ancestry, and is approximately 7.5% for African Americans and 2.1% for European Americans2. African Americans have a disproportionate risk for several forms of CKD, among them diabetic nephropathy3, hypertensive nephrosclerosis4, lupus nephritis5, focal segmental glomerulosclerosis (FSGS) 6 and HIV-associated nephropathy (a distinct form of FSGS, also termed collap-sing glomerulopathy)7 , 8. The disproportionate risk for CKD may be partially explained by differences in social-economic status, lifestyle factors and clinical factors such as blood pressure control, but most of the increased risk remains unexplained9.FSGS is a clinical syndrome involving podocyte injury and glomerular scarring, and includes genetic forms with autosomal dominant or recessive mendelian inheritance, reactive forms associated with other illnesses (including HIV-1 disease) or medications, and a sporadic, idiopathic form, which accounts for the majority of cases 10 . Recent data suggest an increase in the incidence of FSGS, which currently accounts for up to 3% of ESKD cases6. African Americans have a fourfold increased risk for sporadic FSGS11 and an 18-to 50-fold increased risk for HIV-1-associated FSGS7 ,12 . Individuals of African descent also have increased risk for FSGS in other geographic regions, further suggesting that genetic factors contribute to these disparities 11 .A strategy for identifying genes underlying such ancestry-driven health disparities is mapping by admixture linkage disequilibrium (MALD). MALD has successfully identified a genomic region associated with prostate cancer 13 subsequently replicated by a genome-wide association study14, as well as genes associated with hypertension15, multiple scl...

Hypertension affects one billion people and is a principal reversible risk factor for cardiovascular disease. A rare Mendelian syndrome, pseudohypoaldosteronism type II (PHAII), featuring hypertension, hyperkalemia, and metabolic acidosis, has revealed previously unrecognized physiology orchestrating the balance between renal salt reabsorption versus K+ and H+ excretion1. We used exome sequencing to identify mutations in Kelch-like 3 (KLHL3) or Cullin 3 (CUL3) in 41 PHAII kindreds. KLHL3 mutations are either recessive or dominant, while CUL3 mutations are dominant and predominantly de novo. CUL3 and BTB-Kelch proteins such as KLHL3 are components of Cullin/RING E3 ligase complexes (CRLs) that ubiquitinate substrates bound to Kelch propeller domains2–8. Dominant KLHL3 mutations are clustered in short segments within the Kelch propeller and BTB domains implicated in substrate9 and Cullin5 binding, respectively. Diverse CUL3 mutations all result in skipping of exon 9, producing an in-frame deletion. Because dominant KLHL3 and CUL3 mutations both phenocopy recessive loss-of-function KLHL3 mutations, they may abrogate ubiquitination of KLHL3 substrates. Disease features are reversed by thiazide diuretics, which inhibit the Na-Cl cotransporter (NCC) in the distal nephron of the kidney; KLHL3 and CUL3 are expressed in this location, suggesting a mechanistic link between KLHL3/CUL3 mutations, increased Na-Cl reabsorption, and disease pathogenesis. These findings demonstrate the utility of exome sequencing in disease gene identification despite combined complexities of locus heterogeneity, mixed models of transmission, and frequent de novo mutation, and establish a fundamental role for KLHL3/CUL3 in blood pressure, K+, and pH homeostasis.

Analysis of patients with inherited hypokalaemic alkalosis resulting from salt-wasting has proved fertile ground for identification of essential elements of renal salt homeostasis and blood-pressure regulation. We now demonstrate linkage of this phenotype to a segment of chromosome 1 containing the gene encoding a renal chloride channel, CLCNKB. Examination of this gene reveals loss-of-function mutations that impair renal chloride reabsorption in the thick ascending limb of Henle's loop. Mutations in seventeen kindreds have been identified, and they include large deletions and nonsense and missense mutations. Some of the deletions are shown to have arisen by unequal crossing over between CLCNKB and the nearby related gene, CLCNKA. Patients who harbour CLCNKB mutations are characterized by hypokalaemic alkalosis with salt-wasting, low blood pressure, normal magnesium and hyper- or normocalciuria; they define a distinct subset of patients with Bartter's syndrome in whom nephrocalcinosis is absent. These findings demonstrate the critical role of CLCNKB in renal salt reabsorption and blood-pressure homeostasis, and demonstrate the potential role of specific CLCNKB antagonists as diuretic antihypertensive agents.