However, hypercalcemia was considered to be the effect and not the cause of polyuria because (1) serum calcium levels were mildly elevated after overnight dehydration but normalized when the patient was in a hydrated state and after the institution of desmopressin therapy, and (2) a large increase in urine osmolality was seen following arginine vasopressin injection which favors arginine vasopressin deficiency rather than resistance. This evidence concerns the gene AVP and neurohypophyseal diabetes insipidus.