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?

The child has nephronophthisis, the most common genetic cause for end-stage renal disease in children and adolescents, and transmitted in autosomal recessive pattern. The NPHP1 to NPHP11 genes encode for proteins found in the primary cilia, attached ciliary basal bodies, or the centrosome organelle, from which the basal bodies originate. There is a loss of concentrating ability and renal tubular acidosis. MCKD1 mutations are associated with the adult medullary cystic disease with the autosomal dominant transmission. PKD1 encodes for polycystin-1, associated with autosomal dominant polycystic kidney disease (ADPKD). PKHD1 mutations encode for fibrocystin and is associated with autosomal recessive polycystic kidney disease (ARPKD).