ESPE Abstracts

Background: Congenital nephrogenic diabetes insipidus is a rare disease that is sometimes diagnosed after failure to thrive or febrile illness during infancy. Long-term habitual polydipsia to compensate for polyuria is sometimes difficult to distinguish from habitual polydipsia and polyuria or compulsive drinking.

Case: The case is a 10-year-old girl. Her father was diagnosed as having congenital nephrogenic diabetes insipidus (CNDI) at the age of 12 (details unknown). At her birth, the parents were told from the obstetrician that CNDI was X-linked inheritance and female would not show any symptoms, thus both parents did not pay attention on CNDI although the child has been showing polydipsia, polyuria, and fever. Her mother, however suspected dehydration and urged her drinking water; her fever subsided. Her water intake increased to 3-4L /day from around the age of 1 to 2 years old, and had 2 to 3 times urination during night. She was referred to us for further workup when she was 10 years old. During hospitalization, her ad lib total fluid intake and urine output was about 4 L/day. Her abdominal ultrasonography revealed right hydronephrosis (SFU grade 2). Her urine specific gravity was 1.001 and a urine osmolarity 75 mOsm/L. Plasma AVP level was 3.8 pg/ml. Water deprivation test was performed and plasma osmolality reached to plateau at 282 mOsm/L with partial concentration of urine (urine osmolality of 429 mOsm/L at the 7th hour) of along with a weight loss of -1.4 kg (4.8%). In the subsequent Pitressin loading test, the increase in urine osmolality was only up to 453 mOsm/L. In order to exclude abitual polydipsia from partial NDI, genetic test was performed and pathogenic heterozygous variant in AQP2 gene (721del) was found, which confirmed the diagnosis of NDI.

Discussion/Conclusion: We report the familial case with NDI. The clinical manifestation was moderate in proband and the diagnosis was delayed. Partial urine concentration was observed in water deprivation test, which could be observed in habitual polyuria and polydipsia. Given these ambiguous clinical findings, genetic testing was essential to confirm the diagnosis of NDI.