Fei Ding Nie Xin Yuemei Chen Minjin Wang He Yong ^*

• Department of Laboratory Medicine, West China Hospital, Sichuan University, Chengdu, China

Background: Congenital nephrogenic diabetes insipidus (NDI) primarily arises from an X-linked recessive inheritance caused by mutations in the AVPR2 gene and, which is responsible for approximatelyabout 90% of cases. This condition has an incidence rate of 4 to 8 per million male live births, with females being much less frequently affected [1] . Symptoms typically manifest shortly after birth, predominantly in males. The key clinical features of NDI includeencompass excessive urination (polyuria), compensatory excessive thirst (polydipsia), persistent thirst, cognitive impairment, consistently low urine specific gravity, dehydration, and imbalances in electrolyte levels [2] . Case presentation: This case study highlights an unusual occurrence of NDI in a 50-year-old Chinese woman attributed to a mutation in the AVPR2 gene.For more than a year, she had been suffering from excessive urination and severe thirst. The patient, who had undergone surgery for cervical cancer, developed polyuria and hypernatremia post-operatively. Initial laboratory analyses revealedindicated normal blood sodium and chloride levels but revealed reduced urine osmolality and specific gravity. Imaging assessments revealedshowed no irregularities. To validate the diagnosis of NDI, she participated in a water deprivation and vasopressin test. Subsequent genetic tests revealed a thymine (T) to adenine (A) mutation, leading to a missense mutation in the AVPR2 gene. As part of her treatment, she was placed on a low-sodium diet and prescribed oral hydrochlorothiazide and indomethacin for one month, resulting in marked improvement in her symptoms. To the best of our knowledge, this ismarks the first documented case of NDI diagnosed postoperatively in an older female patient with AVPR2 heterozygosity.This case highlights an unusual instance of an X-linked recessive clinical presentation of NDI in an elderly female patient. This studyIt also underscores the importancesignificance of conducting water deprivation, vasopressin tests, and genetic testing in establishing the underlying cause for individuals diagnosed with NDI.