An infant with chronic hypernatremia

A 4-month-old boy was presented with failure to thrive, refusal to feed, delayed motor development, truncal hypotonia, and head lag. His plasma osmolality and sodium were significantly high, while his urine osmolality was inappropriately low and did not increase after desmopressin administration. Despite his hyperosmolality, he presented with a lack of thirst and became clearly polyuric and polydipsic only at the age of 2 years. Initial treatment with indomethacin was ineffective, while the combination of hydrochlorothiazide and amiloride was effective and well tolerated.