Nephrogenic Syndrome of Inappropriate Antidiuresis: Case Report and Genetic Perspectives

To report a case of nephrogenic syndrome of inappropriate antidiuresis (NSIAD) caused by a de novo hemizygous hotspot variant (c.409C>T p.R137C) in the AVPR2 gene in a young male child, and to discuss the diagnostic approach, therapeutic management, and follow-up of NSIAD.

A 3-year and 2-month-old male child presenting with intermittent convulsions persisting for over one year and chronic hyponatremia was clinically evaluated. Genetic testing was performed to identify potential causative variants. Water restriction therapy was implemented, with the patient spontaneously limiting water intake to prevent infections and regulating fluid intake during illnesses. Follow-up evaluations were conducted at 3 and 6 months.

Genetic testing identified a de novo hemizygous hotspot variant, c.409C>T (p.R137C), in the AVPR2 gene. The patient adhered to spontaneous water restriction and regulated fluid intake during illnesses. Follow-up evaluations at 3 and 6 months demonstrated normal serum sodium levels, with no recurrence of convulsions or other symptoms.

NSIAD should be included in the differential diagnosis of hyponatremia of unknown etiology. Genetic testing is crucial for achieving an early diagnosis, optimizing treatment regimens, and enhancing treatment compliance. Water restriction therapy, under careful monitoring, remains a safe and effective treatment modality, particularly during periods of illness.