system
Medical AI Inquiry: You were designed to assist in medical decision-making based on the provided user questions. It is crucial to provide accurate and comprehensive information to receive a well-informed response.
user
A 5-year-old boy is brought to the clinic for recurrent bedwetting. The child has an intellectual disability; thus, the mother is providing most of the history. She states that the child constantly drinks fluids and has a difficult time making it to the bathroom as often as he needs. Therefore, he sometimes wets himself during the day and at night. She has tried bedwetting alarms with no success. Review of systems is negative. His past medical history is unremarkable expect for moderate growth retardation. His temperature is 99.5°F (37.5°C), blood pressure is 80/54 mmHg, pulse is 90/min, respirations are 20/min, and oxygen saturation is 99% on room air. Routine laboratory tests and a 24 hour urine test are shown below.

Serum:
Na+: 138 mEq/L
Cl-: 90 mEq/L
K+: 2.5 mEq/L
HCO3-: 35 mEq/L 
BUN: 9 mg/dL 
Glucose: 98 mg/dL
Creatinine: 1.0 mg/dL
Thyroid-stimulating hormone: 1.2 µU/mL
Ca2+: 9.1 mg/dL
AST: 13 U/L
ALT: 10 U/L
pH: 7.49

Urine:
Epithelial cells: 5 cells
Glucose: Negative
WBC: 0/hpf
Bacterial: None
Protein: 60 mg/24h (Normal: < 150 mg/24h)
Calcium: 370 mg/24h (Normal: 100-300 mg/24h)
Osmolality 1600 mOsmol/kg H2O (Normal: 50-1400 mOsmol/kg H2O)

What is the most likely explanation for this patient’s findings?
assistant
Defect of Na+/K+/2Cl- cotransporter at the thick ascending loop of Henle