AQP2 and Down syndrome: Several techniques have been developed to quantify urine aquaporin-2, such as radioimmunoassay, Western blotting, and sandwich enzyme-linked immunosorbent assay [7,9,10], and urine aquaporin-2 has been quantified in various clinical conditions including pregnancy [11], liver cirrhosis [12], syndrome of inappropriate secretion of antidiuretic hormone [5], diabetes insipidus [4], and HF [13,14].