Renal aging primarily manifests as declining glomerular GFR, impaired sodium balance in the renal tubules, impaired fluid balance, potassium retention, declining urine dilution, decreased ability to reduce urinary pH, decreased effective renal plasma flow, increased filtration fraction, increasing glomerular vascular resistance, impaired vasodilator response, and endocrine-associated changes, including decreased plasma renin and aldosterone, decreased response of EPO to anemia, and decreased vitamin D activity [5,6]. The gene discussed is REN; the disease is anemia (phenotype).