A 6-year-old child has been drinking more water, with more frequent urination, for the past 7 months. On physical examination, dehydration is noted. Urinalysis findings include a pH of 6.5; specific gravity, 1.010; and no protein, blood, glucose, or ketones. There are no WBCs, RBCs, or casts. Serum electrolytes show Na+, 152 mmol/L; K+, 4.6 mmol/L; Cl-, 120 mmol/L; HCO3-, 21 mmol/L; urea nitrogen, 29 mg/dL; and creatinine, 3.2 mg/dL. An ultrasound scan shows bilaterally small kidneys with barely visible medullary cysts concentrated at the corticomedullary junction. Which of the following genes is most likely mutated in this child?
MCKD1 NPHP1 PKD1 PKHD1