The case of an 8 year old boy with both nocturnal enuresis and nephrogenic diabetes insipidus is presented. Diagnosis of nephrogenic diabetes insipidus was based on a typical medical history, the characteristic result of a fluid restriction test, the lack of an effect of 1-desamino-8-D-arginine (DDAVP) on both urine osmolality and plasma coagulation factors and, finally, the detection of a hemizygous missense mutation within the arginine vasopressin (AVP) receptor gene. Hydrochlorothiazide treatment and dietary measures reduced the patient's urine volume to one third of its original volume. However, this had no effect on enuresis. The daily intranasal application of DDAVP did not further reduce urine output but dramatically decreased the frequency of bed wetting. This observation contradicts the common notion that the therapeutic effect of DDAVP in nocturnal enuresis is the result of compensation for a nocturnal AVP deficit. Rather, it points to a different mode of action of DDAVP in patients with enuresis. It is hypothesised that central AVP receptors are a target of DDAVP and that they might play an important role in the pathogenesis of nocturnal enuresis.
