USMLE (United States Medical Licensing Examination) Practice Exam 08

A 24-year-old woman comes to the clinic because of intermittent muscle weakness and palpitations for 2 months. She reports frequent episodes of lightheadedness after long runs. She takes no medications. Blood pressure is 108/66 mm Hg. Physical examination is unremarkable. Laboratory studies show: Na+ 141 mEq/L, K+ 2.8 mEq/L, Cl− 88 mEq/L, HCO3− 34 mEq/L, BUN 10 mg/dL, creatinine 0.7 mg/dL. Urine chloride is 52 mEq/L (elevated). Which of the following is the most likely underlying renal tubular transport abnormality?