In patients with CKD, there was a very strong positive correlation between serum cystatin C and serum creatinine (r = 0.90), and both biomarkers showed a strong negative correlation with eGFRCr-Cys (r ≈ -0.90), indicating that as eGFR decreases, both biomarker levels increase. The gene discussed is CST3; the disease is chronic kidney disease.