A Novel Pathogenic Variant of the Gene Leading to Arginine Vasopressin Resistance Since the Neonatal Period.

: Diabetes insipidus (DI) in newborns is an extremely rare condition, with the age of presentation strongly suggesting a genetic background of the disease. The differential diagnosis should include arginine vasopressin deficiency (AVD) and arginine vasopressin resistance (AVR). Some novel diagnostic tools such as copeptin evaluation and genetic tests are vital for early diagnosis. : We present the case of a 1-month-old boy with polyuria observed since birth. Laboratory tests showed persistent hypernatremia, elevated plasma and low urine osmolality. An attempt at oral administration of desmopressin had no effect; additionally the copeptin level was increased. A genetic study (NGS of the , and genes) was considered and a new pathogenic variant in the gene (hemizygous c.157del) was detected. After the genetic test result was obtained, treatment with hydrochlorothiazide was started. The patient is now 3 months old, developing normally, and the weight and height are normal. : Newborns with DI should be subjected to extensive multidisciplinary diagnostics, including endocrine and renal causes. Copeptin evaluation and prompt genetic diagnosis allows for the early diagnosis and implementation of appropriate treatment.