rs4961 — ADD1 Gly460Trp

ADD1 Gly460Trp — The Salt-Pressure Switch in Your Kidneys

Alpha-adducin is a cytoskeletal protein that does something quietly consequential in your kidney tubules: it controls how many sodium pumps sit active at the cell surface. The ADD1 gene (adducin 1)¹¹ ADD1 gene (adducin 1)
encodes the alpha subunit of the adducin heterotrimer, which links the spectrin-actin cytoskeleton to the plasma membrane and regulates ion transport channel trafficking in kidney cells. When adducin stabilizes the Na+/K+-ATPase²² Na+/K+-ATPase
the sodium-potassium pump that moves three sodium ions out of the cell for every two potassium ions in, establishing the electrochemical gradient that drives secondary sodium transport at the cell surface, more sodium gets reabsorbed from the tubular filtrate back into the bloodstream — raising blood volume and, with it, blood pressure.

The Gly460Trp variant substitutes tryptophan for glycine at position 460 in the protein's tail domain, altering how tightly the pump anchors. About 19% of Europeans carry at least one copy of the Trp allele; in East Asian populations the frequency climbs to 51%, which may partly explain higher rates of salt-sensitive hypertension in those populations.

The Mechanism

At position 460, the normal glycine (Gly) creates a flexible hinge in adducin's tail domain. Substituting tryptophan (Trp) — a bulkier, aromatic amino acid — rigidifies the structure and increases affinity for the Na+/K+-ATPase³³ increases affinity for the Na+/K+-ATPase
the Trp460 isoform stabilizes the pump at the apical membrane of renal proximal tubule cells, increasing its surface density and thus its total sodium transport capacity. More pumps at the surface means more tubular sodium reabsorption.

The consequence unfolds in two kidney compartments. In the proximal tubule, where most filtered sodium is reclaimed, Trp460 adducin increases baseline sodium reabsorption. When a salt load arrives — a salty meal, intravenous saline — the Trp460 kidney retains more of that sodium rather than excreting it, blunting the normal pressure-natriuresis response and causing a steeper, more prolonged blood pressure rise.

The Trp460 variant also impairs endothelial function. In the vasculature, adducin helps organize caveolae — the lipid-raft microdomains where endothelial nitric oxide synthase (eNOS) resides. Disruption of this organization reduces eNOS activation, blunting nitric oxide-dependent vasodilation and adding a vascular component to the hypertension risk.

The Evidence

The vascular consequences are documented in a study of 110 never-treated hypertensive patients⁴⁴ 110 never-treated hypertensive patients
Perticone et al., J Hypertens 2007. Trp allele carriers showed markedly impaired forearm blood flow response to acetylcholine — a test of endothelium-dependent vasodilation — rising only 269% at the highest dose versus 395% in Gly/Gly homozygotes (P<0.001). The response to sodium nitroprusside, which acts independently of the endothelium, was identical between groups, confirming that the deficit is specifically endothelial, not vascular smooth muscle.

Cardiovascular outcomes data come from the Rotterdam Study (6,471 participants)⁵⁵ Rotterdam Study (6,471 participants)
van Rijn et al., Stroke 2006, where Trp allele carriers had a stroke hazard ratio of 1.22 (95% CI 1.02–1.45), ischemic stroke HR 1.29 (95% CI 1.02–1.63), and myocardial infarction HR 1.33 (95% CI 1.05–1.69). Carotid intima-media thickness was modestly increased in carriers (0.80 vs 0.79 mm, P=0.04). Critically, the interaction between the Gly460Trp polymorphism and hypertension was statistically significant — the risk was amplified in those who were also hypertensive, linking the molecular sodium-retention mechanism to hard cardiovascular outcomes.

For pharmacogenomics, a meta-analysis of 4 studies (1,001 patients)⁶⁶ meta-analysis of 4 studies (1,001 patients)
Choi et al., Int J Clin Pharmacol Ther 2013 found that the GlyGly genotype achieved significantly greater blood pressure reduction on hydrochlorothiazide than TrpTrp homozygotes (standard difference 1.80, 95% CI 1.38–2.22). The sodium-retaining effect of Trp460 adducin partially offsets the diuretic's mechanism, which also targets tubular sodium transport.

A Ukrainian cohort study (2024)⁷⁷ Ukrainian cohort study (2024)
Sydorchuk et al., Endocr Regul confirmed that T-allele carriers in hypertensive patients had approximately 4-fold higher odds of being sodium-sensitive — women OR 4.71 (95% CI 1.92–11.56, P<0.001) and men OR 4.09 (95% CI 1.03–16.28, P=0.041).

Practical Actions

For Trp allele carriers — particularly TT homozygotes — the most actionable intervention is aggressive dietary sodium restriction. Unlike the general population, where blood pressure response to sodium reduction is variable, carriers of the Trp460 allele have a documented biological mechanism that makes sodium reduction disproportionately effective.

Hydrochlorothiazide, the most commonly prescribed first-line antihypertensive, works less well in Trp carriers because both the drug and adducin act on overlapping tubular sodium transport pathways. If hypertension requires pharmacotherapy, ACE inhibitors, ARBs, or renin-angiotensin-aldosterone system agents may be pharmacologically better matched to this genotype.

Monitoring endothelial function through blood pressure response tracking and periodic cardiovascular risk assessment is warranted for TT homozygotes, who face the combination of both renal sodium retention and impaired vasodilation.

Interactions

The ADD1 Trp460 allele functions as a permissive variant in the renal sodium handling network. A physiological interaction study involving ADD1 (rs4961), WNK1, and NEDD4L (rs1008899/rs4149601) found that the ADD1 Trp allele is required for the effects of the other variants to manifest — individuals carrying risk alleles at all three loci showed the most pronounced sodium retention, the highest blood pressure on saline loading (P=0.021), and the greatest response differential to thiazide therapy (P=0.008). This axis — ADD1 → WNK1 → NEDD4L → ENaC — represents a coherent sodium-retention pathway where each node amplifies the others' effects.

The interaction with endogenous ouabain (a naturally occurring Na+/K+-ATPase inhibitor circulating at low levels in plasma) is also documented: Trp460 carriers with elevated ouabain showed the largest blood pressure rises on volume loading, suggesting adducin-ouabain co-regulation of pump density.