ODP279 A Case of Nephrogenic Diabetes Insipidus Diagnosed at an Advanced Age in a Female Patient with an AVPR2 Gene Mutation and Skewed×Inactivation

BACKGROUND: Arginine vasopressin receptor 2 (AVPR2) gene mutationsare the most common cause of congenital nephrogenic diabetes insipidus (CNDI), and they are inherited in an X-linked recessive manner. Women are generally asymptomatic or mildly affected, but atypically severe cases have been reported. Skewed X inactivation, in which the X chromosome is unevenly active, is a cause of this atypical severe case.×chromosome inactivation is a developmental compensation mechanism that results in equal doses of X-linked genes between XX females and XY males and has been reported to be accentuated by aging. CLINICAL CASE: A 69-year-old woman had no family history of diabetes insipidus. Immediately after undergoing a craniotomy for subarachnoid hemorrhage in July, she showed marked polyuria of approximately 8000 mL/day and hypernatremia of 161 mEq/L. The use of desmopressin (15mcg/kg/day) did not improve herpolyuria. She was referred to our department in September for further investigation and treatment. Her urine osmolality remained hypotonic at approximately 60–80 mOsm/kg/H 2 O (50–1300 mOsm/kg/H 2 O) according to a water restriction test. Her urine osmolality increased slightly to 106 mOsm/kg/H 2 O in a desmopressin test. These results indicated that desmopressin was ineffective, and the patient was diagnosed with nephrogenic diabetes. Her urine output decreased to approximately 2500 mL/day with trichlormethiazide treatment. There was no significant anterior pituitary hypofunction. Genetic examination revealed a heterozygous mutation of the AVPR2 gene (c.656T>G, p. Leu219Arg) in her X chromosome, and her X chromosome activity ratio was 79: 21 in a human androgen receptor assay, indicating skewed X inactivation. CONCLUSION: We observed a case of CNDI in an elderly woman with no family history of the disease. In this case, a combination of the skewed X inactivation, presumably accentuated by aging, and the onset of subarachnoid hemorrhage, reduced her drinking water and led to the diagnosis of CNDI. References: (1)K. Kinoshita et al, J. Endocrinol. Invest. 27: 167-170, 2004. (2)Ding C et al, Am J Med Genet Part A. 2020; 182A: 1032–1040. (3)Y. Nomura et al, Journal of Clinical Endocrinology and Metabolism: 3434-3437, 1997. Presentation: No date and time listed