An 8 years old child suffering from recurrent attacks of polyuria since childhood presents to the pediatrics OPD. On examination, the child has short stature. Vitals and B.P. are normal. S. Creatinine - 6 mg/dL, HCO3 - 16 meq/L, S Na+ - 134 meq/L. On USG, bilateral small kidneys are seen. Diagnosis is: