Introduction: Nephrogenic syndrome of inappropriate antidiuresis (NSIAD) is an uncommon X-linked genetic condition marked by euvolemic hyponatremia, which arises from a gain-of-function mutation in the arginine vasopressin receptor type 2 (AVPR2) gene. In contrast to the classic syndrome of inappropriate antidiuretic hormone secretion (SIADH), NSIAD is characterized by urine that is inappropriately concentrated even when arginine vasopressin (AVP) levels are low or undetectable. Failure to recognize NSIAD may result in recurrent hyponatremia and neurological morbidity. Case: A 2-year-old male was referred to us after recurrent vomiting and subsequently developed generalized tonicclonic seizures due to hyponatremia (with a sodium level of 115 mmol/L). He needed sodium replacement through an intravenous drip of 3% saline and was stabilized with oral sodium chloride 20%. Urine osmolality was elevated, serum osmolality remained normal, and copeptin levels were low. He was discharged after a 10-day hospital stay. During follow-up, hyponatremia recurred despite his typical fluid intake of 1,200 mL/day. He was instructed to limit his fluid intake to 600–700 mL, which successfully normalized his serum sodium levels. Serum levels of adrenocorticotropic hormone, the aldosterone-to-renin ratio, thyroid function tests, and serum cortisol were all within normal ranges. Plasma AVP was unusually low (4.0 pmol/L). Whole exome sequencing (WES) confirmed a likely pathogenic hemizygous variant in AVPR2 gene located on chromosome Xq28, which was inherited from his mother. He is the only child, born from a non-consanguineous marriage, with no other significant family medical history. Conclusion Nephrogenic syndrome of inappropriate antidiuresis (NSIAD), is an uncommon, yet clinically significant condition. This case highlights the importance of considering a broad range of differential diagnoses when a patient presents with hyponatremic seizure. Furthermore, obtaining a detailed family history is essential to identify potential hereditary factors that could contribute to the condition and for genetic counseling.
Child ; Nephrogenic Syndrome of Inappropriate Antidiuresis