Endocrine Abstracts

X-linked nephrogenic diabetes insipidus (NDI) is a rare hereditary condition characterised by renal resistance to arginine vasopressin (AVP). Diagnosis can pose clinical challenges, but molecular genetic analysis can offer a swift and conclusive diagnosis. Herein, we present the case of a 13-year-old boy born from a non-consanguineous marriage, underwent appendicitis surgery at our hospital. Post-procedure, on the first day, the child was found to have severe hypernatremia (180 mmol/l). Subsequent assessment revealed that the child had been experiencing polyuria and polydipsia since the age of two, although no medical consultation had been sought for these symptoms. Further assessment revealed elevated serum osmolarity (370 mosm/kg) accompanied by decreased urine osmolarity (218 mosm/kg). Despite vasopressin stimulation, there was no improvement in urine osmolarity, supporting the diagnosis of nephrogenic diabetes insipidus. Clinical exome sequencing confirmed a hemizygous 28-base pair duplication in exon 3 of the AVPR2 gene, resulting in a frameshift and premature truncation of the protein 182 amino acids downstream from codon 19 (p.Leu19ArgfsTer182). This mutation, located on the X chromosome, can lead to X-linked recessive NDI. Notably, the p.Leu19ArgfsTer182 mutation of the AVPR2 gene has not been previously documented in the literature. The child was discharged while on a combination of thiazide and amiloride, which led to significant improvement in his clinical condition. This case report underscores the clinical and molecular features of a newly identified mutation in AVPR2, resulting in congenital nephrogenic diabetes insipidus (CNDI). It highlights the crucial role of achieving a definitive diagnosis in patients with CNDI.