Anesthesia 5 Jan (M) 2026

A male child with self-mutilation, neurological dysfunction, hyperuricemia, and dystonia. A deficiency of which enzyme is responsible?

A 28-year-old man presents with excessive thirst and passing large volumes of urine (7-8 L daily) for three months. Investigation reveals serum sodium of 150 mEq/L and increased serum osmolarity, while urine osmolarity is 210. Urine remains diluted after water restriction, but after giving a CNS analog like desmopressin, urine osmolarity increases significantly. What is the diagnosis?