ESPE Abstracts

Background: Nephrogenic diabetes insipidus (NDI) is a disorder characterized by renal resistance to the antidiuretic effect of AVP. Affected patients are exhibiting symptoms as polyuria and polydipsia. Approximately 90% of congenital NDI are inherited in an X-linked recessive manner and caused by mutations of arginine vasopressin type 2 receptor (AVPR2) gene.

Objective and hypotheses: An 8-year-old Japanese boy was referred to our hospital for nocturnal enuresis and polydipsia from infancy. He was habitually drinking 3.3–4.0 l liquids/day and urinating 2.8–3.0 l/day. His younger brother, his mother and his mother-side uncle also have polydipsia and polyuria. We suspect him as congenital NDI.

Method: We performed the water deprivation test following DDAVP administration and the hypertonic saline test. We also analysed the genomic DNA for mutations in AVPR2.

Results: On the water deprivation test following DDAVP administration, his peak urine osmolality increased to 546 mOsm/l, and it proved that his renal tubule had responded to AVP. However throughout the entire test, basal AVP level were high nevertheless his serum osmolality is within normal range. On the hypertonic saline test, his serum osmolality and ADH level raised to 292 mmHg and 16.4 pg/dl. These results strongly suggested that his partial renal AVP resistance. The genomic DNA was analysed for mutations in AVPR2 and we identified a novel missense mutation (L161P) in the patient and his mother was heterozygous for the mutation.

Conclusion: In the clinical practice, it is not simple to diagnose the partial NDI. The DNA analysis was useful to diagnose partial NDI. Nocturnal enuresis is one of the most common diseases in children, and it is important to perceive the underlying disease.