rs4293393 — UMOD

UMOD Promoter Variant — When Kidney Protection Comes at a Cost

The UMOD gene encodes uromodulin¹¹ uromodulin
Also called Tamm-Horsfall protein, uromodulin is the most abundant protein in normal human urine, produced exclusively by cells lining the thick ascending limb of the loop of Henle, a protein with a paradoxical dual role in kidney health. Uromodulin forms protective filaments in urine that trap bacteria and prevent urinary tract infections²² trap bacteria and prevent urinary tract infections
Uromodulin polymerizes into filaments that bind type 1 fimbriae on uropathogenic E. coli, blocking their attachment to the bladder wall, but it also activates sodium reabsorption in the kidney, driving up blood pressure. The rs4293393 variant sits in the UMOD promoter region³³ UMOD promoter region
Located 550 base pairs upstream of the transcription start site, within a glucocorticoid response element, where it controls how much uromodulin your kidneys produce — and more is not always better.

The Mechanism

The rs4293393 risk allele (A on the plus strand, reported as T in the medical literature since UMOD is on the minus strand) sits within a glucocorticoid response element⁴⁴ glucocorticoid response element
A DNA sequence where glucocorticoid receptor proteins bind to regulate gene transcription in the UMOD promoter. The risk allele approximately doubles promoter activity⁵⁵ doubles promoter activity
Luciferase reporter assays showed ~2-fold higher transcription with the risk allele across multiple kidney cell lines compared to the protective G allele, leading to higher uromodulin production. This excess uromodulin activates the NKCC2 sodium-potassium-chloride cotransporter⁶⁶ NKCC2 sodium-potassium-chloride cotransporter
The key sodium reabsorption channel in the thick ascending limb of the loop of Henle, activated via SPAK/OSR1 kinase signaling in the thick ascending limb of the loop of Henle, increasing sodium reabsorption and driving salt-sensitive hypertension. The same mechanism causes progressive kidney damage through sustained hemodynamic stress on nephrons.

The Evidence

The UMOD promoter locus is one of the strongest and most replicated GWAS signals for kidney function. A landmark Icelandic study⁷⁷ landmark Icelandic study
Gudbjartsson et al. PLoS Genetics 2010 — 3,203 CKD cases and 38,782 controls from deCODE found the risk allele conferred CKD susceptibility with OR 1.25 (P = 4.1 x 10⁻¹⁰), while paradoxically protecting against kidney stones (OR 0.88, P = 5.7 x 10⁻⁵). A critical finding was that the effect on serum creatinine is strongly age-dependent⁸⁸ strongly age-dependent
Negligible before age 50 but accelerating rapidly after, at ~0.09 μmol/L per allele per year — negligible before age 50 but increasing sharply thereafter, particularly in the presence of comorbidities like diabetes and hypertension.

The Framingham Heart Study⁹⁹ Framingham Heart Study
Köttgen et al. JASN 2010 — 200 FHS participants with uromodulin measurements and genotyping demonstrated a striking dose-response: urinary uromodulin concentrations were 5.5 μg/mL with two risk alleles versus just 1.5 μg/mL with two protective alleles, and elevated uromodulin preceded incident CKD (OR 1.72 per SD increase).

The largest study to date, a PheWAS in 648,593 veterans¹⁰¹⁰ PheWAS in 648,593 veterans
Hung et al. Kidney Int Rep 2022 — Million Veteran Program multiethnic biobank from the Million Veteran Program, confirmed CKD risk (OR 1.22), hypertension (OR 1.03), gout (OR 1.04), and demonstrated protective effects against UTIs (OR 0.94) and kidney stones (OR 0.85) — all in non-Hispanic White participants. Notably, these associations were absent or attenuated in Black participants.

Practical Implications

The UMOD risk allele is extraordinarily common — carried by approximately 80% of people of European and African ancestry and over 90% in East Asian populations. This high frequency is maintained by pathogen-driven natural selection¹¹¹¹ pathogen-driven natural selection
Olden et al. JASN 2016 — analysis of 156 worldwide populations showed UMOD risk allele frequency correlates with bacterial diversity and UTI-causing pathogen prevalence: the same allele that increases CKD risk also protects against urinary tract infections, a major cause of morbidity throughout human evolution. The protective allele was found in Neanderthal and Denisovan genomes but has been selected against in modern humans, likely because UTI protection was more immediately advantageous than avoiding late-onset kidney disease.

The strongly age-dependent effect means this variant matters most after age 50, especially in the context of other metabolic risk factors. The mechanism through NKCC2 activation makes this a genuinely salt-sensitive form of hypertension — carriers may respond specifically to loop diuretics¹²¹² loop diuretics
Studies showed the loop diuretic furosemide produced greater blood pressure reduction and natriuresis in homozygous risk carriers compared to non-carriers and sodium restriction.

Interactions

rs4293393 is in near-perfect linkage disequilibrium¹³¹³ near-perfect linkage disequilibrium
r² = 0.95–1.0 in HapMap CEU populations with rs12917707, meaning these two SNPs are effectively the same signal — a person's genotype at one nearly always predicts their genotype at the other. Both tag the same UMOD promoter haplotype. rs13333226 is another SNP in the same LD block with concordant effects on uromodulin expression and CKD risk.

The UMOD mechanism intersects with other kidney function pathways. Variants in SLC22A2 (organic cation transporter, relevant to metformin clearance), SLC34A1 (phosphate transport), and APOL1 (African-ancestry CKD risk) affect kidney function through independent mechanisms and could compound CKD risk when present alongside the UMOD risk allele.