Sodium Glucose Co-Transporter2 (SGLT2) Inhibition for Refractory Hypomagnesemia in Monogenic Diabetes Type 5 (MODY 5)

Background: MODY 5 is an infrequently reported form of monogenic diabetes attributed to deletions of chromosome 17q12 with impaired expression of HNF1β (Hepatocyte Nuclear Factor 1 Beta). We report a patient who presented with hyperglycemia and hypomagnesemia with an eventual diagnosis of MODY5 that responded to treatment with the SGLT2 inhibitor (SGLT2i), canagliflozin. Clinical case: A 64-year-old male diagnosed with diabetes at age 60 and treated with glimepiride and metformin (HbA1c 6.1–6.2% without hypoglycemia) presented to establish care. He had a prior history of hypermagnesuric hypomagnesemia (serum Magnesium (Mg) 1.4 ± 0.3 mg/dl with Fractional Excretion of Mg (FEMg) 32 ± 3% [values >3–4% in the setting of normal renal function and hypomagnesemia indicates renal Mg loss]) that developed while taking Triamterene- HCTZ for hypertension, prompting discontinuation. Treatment with oral and intravenous (IV) Magnesium along with Amiloride failed to normalize serum Mg levels. Genetic evaluation revealed 17q12 deletion consistent with a diagnosis of MODY 5. Referral to nephrology resulted in discontinuation of glimepiride and addition of canagliflozin 100 mg titrated to 300 mg daily. Mg levels normalized (serum Mg level 1.9 ± 0.1 mg/dL) within 8 weeks of canagliflozin therapy, allowing discontinuation of IV Mg and patient reported improvement in physical stamina and quality of life. At his 1 year follow up visit, his serum Mg remains stable at 1.8mg/dl with a FEMg of 22 ± 2.5%. His current therapy includes Metformin 2 gm, Canagliflozin 300 mg, Amiloride 10 mg tid, and oral Mg. Discussion: Prior to introduction of the SGLT2i, MODY 5 patients required oral and IV Mg repletion in combination with amiloride to achieve near normal Mg levels. Several clinical trials with SGLT2i demonstrated dose and agent dependent improvement in Mg levels in patients with type 2 diabetes. Proposed explanations include reductions in eGFR, changes in intraluminal electrical potential, and activation of renin angiotensin aldosterone system. Mg replacement results not only in symptomatic improvement, but has also been demonstrated to reduce risk of stroke and all-cause mortality. In summary, SGLT2 inhibitors in patients with MODY 5 can be effective in restoring normal Mg levels, improving quality of life, and reducing all cause mortality.