rs3755351 — ADD2

ADD2 rs3755351 — Beta-Adducin and the Renal Sodium Set Point

Beta-adducin¹¹ Beta-adducin
encoded by ADD2, one of three adducin subunit genes (ADD1, ADD2, ADD3) is a cytoskeletal protein that heterodimerizes with alpha-adducin to regulate the cortical actin network beneath the plasma membrane of renal tubular epithelial cells. The adducin complex controls how efficiently the sodium-potassium pump (Na+/K+-ATPase) is recycled to and from the cell surface — a mechanism that sets the kidney's baseline rate of sodium reabsorption and, by extension, blood pressure. The intronic variant rs3755351 emerged from the first large-scale Japanese hypertension GWAS as the single SNP with the strongest statistical signal in the entire genome-wide screen.

The Mechanism

In renal proximal tubule cells, adducin anchors Na+/K+-ATPase pumps to the clathrin-mediated endocytic machinery. Normal constitutive endocytosis²² Normal constitutive endocytosis
the baseline recycling of membrane proteins into the cell interior continuously removes a proportion of Na+/K+-ATPase from the cell surface, limiting how much sodium the kidney retakes from the filtrate. Hypertension-associated adducin variants reduce this constitutive endocytosis, keeping more pumps at the membrane and increasing sodium reabsorption — a subtle but persistent upward shift in the blood pressure set point.

rs3755351 lies within an intron of ADD2. Because ADD2 produces multiple splicing isoforms³³ splicing isoforms
different mRNA transcripts from the same gene by including or excluding different exon segments with distinct expression levels in kidney and brain, intronic variants can alter splice-site strength, exon inclusion rates, or regulatory element binding — changing effective ADD2 protein levels in the tissues where blood pressure is set. The precise molecular consequence of rs3755351 has not been characterized at the protein level; its biological plausibility rests on the well-established role of adducin in renal sodium handling and the convergent evidence from the Milan hypertensive rat model.

The Evidence

Kato et al. 2008⁴⁴ Kato et al. 2008 performed a three-tiered genome-wide association study in Japanese subjects (up to 619 hypertensive and 1,406 normotensive individuals in the final tier) and found rs3755351 carried the lowest p-value of all 75 candidate SNPs selected from an initial screen of 80,795 markers (combined p = 1.7×10⁻⁵). The authors explicitly noted that ADD2 was "nominated" as a susceptibility gene for hypertension, pending independent replication.

Mechanistic support comes from cell biology. Torielli et al. 2008⁵⁵ Torielli et al. 2008 demonstrated in renal epithelial cell lines that alpha-adducin mutations reduce constitutive Na+/K+-ATPase endocytosis and that adducin associates directly with clathrin-coated vesicles involved in pump internalization. Bianchi 2005⁶⁶ Bianchi 2005 reviewed the full translational chain from Milan hypertensive rats (which carry adducin mutations) to human association data, describing how adducin polymorphisms increase tubular sodium reabsorption and proposing pharmacogenomic targeting of this pathway with diuretics.

A replication attempt in an African-Brazilian quilombo population⁷⁷ African-Brazilian quilombo population (652 individuals from 97 families) found no significant individual association of rs3755351 with blood pressure. This population-specific null result, combined with the absence of any GWAS Catalog registration for rs3755351, means the hypertension association remains a single-study nomination with limited independent confirmation.

Evidence level is therefore emerging: mechanistically credible, with one genome-wide signal in a specific ancestry group and no large cross-ancestry meta-analytic validation.

Practical Implications

Because rs3755351 is an intronic variant in ADD2 without established clinical utility, carriers of the T allele cannot currently receive guideline-supported medication adjustments based on this SNP alone. The actionable guidance centers on monitoring blood pressure trends and understanding that sodium handling is a core determinant of blood pressure in individuals with adducin pathway variants.

The well-studied alpha-adducin variant rs4961 (ADD1 G460W) has clearer pharmacogenomic data linking adducin carrier status to enhanced thiazide diuretic responsiveness. Carriers of ADD2 rs3755351 risk alleles may share an underlying sodium-retaining physiology that has implications for the same class of antihypertensives, but this is inferential rather than directly demonstrated.

Limiting dietary sodium is the most evidence-supported intervention for sodium-sensitive hypertension, and adducin pathway variants are the best-characterized molecular basis of sodium sensitivity identified through GWAS.

Interactions

ADD2 encodes beta-adducin, which obligately functions as a heterodimer with alpha-adducin (rs4961, ADD1). The ADD1 G460W variant (Trp allele of rs4961) has been independently associated with hypertension and specifically with enhanced blood pressure response to thiazide diuretics in multiple cohorts. Carriers of risk alleles at both ADD1 and ADD2 may have additive impairment of renal Na+/K+-ATPase regulation. The Milan hypertensive rat model, which provided the original mechanistic framework, carries mutations in both alpha- and beta-adducin subunits, suggesting that compound genotypes across ADD1 and ADD2 may have stronger combined effects on sodium reabsorption than either variant alone.