This may explain why in our initial review of children with HNF1B mutations, hypokalemia was not noted as a specific feature, whereas in a review of adult patients, approximately half were noted to have hypokalemia with renal potassium wasting, even despite worsening eGFR.6, 12 Hypomagnesemia may contribute to hypokalemia, as lack of intracellular magnesium unblocks the secretory potassium channel KCNJ1.18 The gene discussed is KCNJ1; the disease is familial primary hypomagnesemia.