Long-Term Validation of E-selectin Gene S128R Polymorphism as a Predictor of Cyst Growth in Autosomal Dominant Polycystic Kidney Disease

Technical Summary: Long-Term Validation of E-selectin Gene S128R Polymorphism as a Predictor of Cyst Growth in Autosomal Dominant Polycystic Kidney Disease

Problem Statement
Autosomal Dominant Polycystic Kidney Disease (ADPKD) is a leading inherited cause of end-stage kidney disease, characterized by progressive cyst formation, total kidney volume (TKV) expansion, and gradual renal function decline. While the disease is driven by PKD1 or PKD2 mutations, recent evidence suggests that endothelial dysfunction and chronic inflammation contribute to its progression. E-selectin, an adhesion molecule upregulated during endothelial activation, has been implicated in this pathophysiology. However, the long-term prognostic value of serum E-selectin levels and the specific impact of the SELE S128R (rs5361) gene polymorphism on structural and functional disease progression in ADPKD remain unclear. Previous short-term studies yielded inconclusive results regarding the association between this polymorphism and cyst growth.

Methodology
This study represents a 10-year prospective longitudinal follow-up of a previously established ADPKD cohort.

• Cohort: From an initial baseline cohort of 76 patients, 20 patients with complete 10-year follow-up data were included in the final analysis. Exclusions were due to loss to follow-up, transfer to other centers, initiation of renal replacement therapy, or death.
• Genotyping: The SELE S128R polymorphism was analyzed using Polymerase Chain Reaction–Restriction Fragment Length Polymorphism (PCR-RFLP). Patients were stratified into two groups: the wild-type AA genotype (n=13) and variant carriers (AC + CC genotypes, n=7).
• Data Collection:
  • Structural Imaging: Total Kidney Volume (TKV), height-adjusted TKV (htTKV), and dominant renal cyst volumes were assessed via T2-weighted Magnetic Resonance Imaging (MRI) at baseline and at the 10-year mark. The Mayo Imaging Classification was used for risk stratification.
  • Biochemical Analysis: Serum E-selectin levels were measured via ELISA. Comprehensive biochemical panels included renal function markers (creatinine, eGFR, urea), mineral metabolism (PTH, calcium, phosphorus), and inflammatory/metabolic markers.
  • Statistical Analysis: Due to the small sample size (n=20) and non-normal distribution of variables, non-parametric methods were employed. The Wilcoxon signed-rank test compared baseline vs. follow-up within groups, and the Mann–Whitney U test compared differences between genotype groups. Spearman's rank correlation assessed associations between variables.

Key Results

• Overall Disease Progression: Over the 10-year period, the entire cohort exhibited significant disease progression. TKV and htTKV increased significantly (p=0.001 for both). Left dominant cyst volume increased significantly (p=0.013), while right dominant cyst volume showed a non-significant trend. Renal function deteriorated, evidenced by a significant rise in serum creatinine (p=0.022) and a significant decline in eGFR (p=0.002).
• Genotype-Specific Findings:
  • AA Genotype: Patients with the AA genotype demonstrated significant longitudinal increases in TKV and htTKV (p=0.008 for both). They also showed significant increases in left and right dominant cyst volumes, as well as significant worsening in renal function markers (creatinine p=0.023, eGFR p=0.009) and parathyroid hormone levels (p=0.021).
  • AC + CC Genotypes: In contrast, the variant carrier group (AC + CC) did not show statistically significant changes in TKV, htTKV, or renal function markers over the 10-year period (all p > 0.05).
  • Baseline Differences: No significant differences were observed between the AA and AC+CC groups regarding baseline demographic, radiological, or biochemical parameters.
• Serum E-selectin Levels: Baseline serum E-selectin levels remained stable over the 10-year period for the total cohort and within both genotype groups. No significant correlation was found between baseline E-selectin levels and changes in TKV, htTKV, cyst volumes, or eGFR. However, baseline E-selectin levels did show a positive correlation with changes in creatinine (r=0.530, p=0.042) and PTH (r=0.541, p=0.046).

Significance and Claims
The authors claim that this study provides long-term validation of the SELE S128R polymorphism as a potential predictor of disease progression in ADPKD, specifically highlighting the AA genotype as being associated with more pronounced structural (cyst and kidney volume) and functional (renal function decline) deterioration over a decade.

Key contributions and conclusions include:

1. Genetic Susceptibility: The AA genotype of the SELE S128R polymorphism is associated with significant longitudinal changes in TKV, htTKV, and dominant cyst volume, as well as renal functional decline, whereas variant carriers (AC/CC) did not exhibit these significant changes.
2. Biomarker Limitations: While endothelial dysfunction is a known factor in ADPKD, circulating serum E-selectin levels alone do not appear to be a sufficient marker for predicting long-term cyst progression or structural changes in this context.
3. Multifactorial Nature: The findings suggest that while genetic variation in endothelial inflammatory regulators (like SELE) may influence disease susceptibility and progression rates, the disease trajectory is shaped by complex, multifactorial mechanisms beyond simple circulating adhesion molecule levels.

The authors acknowledge limitations, primarily the small final sample size (n=20) resulting from a high attrition rate from the original cohort, which may limit statistical power. They conclude that while their findings suggest a genetic contribution to disease susceptibility, larger-scale studies with functional analyses are required to confirm the clinical significance of the SELE S128R polymorphism in ADPKD management.