Endocrine Abstracts

Background and aims: Patients with AVPR2 gene mutations present nephrogenic diabetes insipidus (NDI) resulting to a severe deficit in urine concentration despite high levels of circulating Antidiuretic Hormone (ADH). The mutation in codon 106 of the AVPR2 gene leading to the substitution of arginine by cysteine (R106C) is known to produce a mild disease while in vitro characterization revealed a complete loss of function. We report the case of a 24-year-old male member of an Algerian family with the R106C mutation. His work and social life was severely affected by a polyuria of 6 l of urine per day. He presented hydro ureteronephrosis and hypotonic enlarged neurogenic bladder needing 7 to 8 intermittent characterizations on a daily basis. He was referred to our clinic for a desmopressin (dDAVP) urine concentration test.

Materials and methods: Blood and urine samples were collected hourly for a period of 6 h. The patient received 2 dDAVP (4 μg) subcutaneous injections at *60 and **180 min. Baseline ADH values were at 27 pg/ml (Reference values: 1.9–2.1).

Results: The rise in urine osmolality, the negativation of free water clearance, the rise in nephrogenic AMPc shows in vivo that the R106C mutation is responsive to dDAVP. Hence assuming a mean urine osmolality of 300 mOsm/l under dDAVP treatment the urine output could be limited to less than 3 l.

Conclusion: This case emphasizes that the R106C mutation can present with urological complications and that dDAVP test is useful to predict patient response to treatment in the case of partial NDI.