A case of Fanconi syndrome associated with insulin-resistant diabetes mellitus and carnitine deficiency

A 46-year-old woman admitted for hypokalemia had been emaciated since 15 years old and was diagnosed with renal glucosuria at 21 years and borderline GTT at 35 years. She developed gestational diabetes at 38 years, and a Caesarean section was conducted at 29 weeks of gestation, while her blood glucose was controlled by 62 units of insulin per day. After the delivery, her glycemia was controlled by diet alone, but 75 g OGTT showed a diabetes mellitus pattern and hyperinsulinemic response (before, 7.7 μU/ml; 120 min, 149.4 μU/ml). At 46 years old, her body mass index was 13.3 kg/m². Renal tubular function tests showed panaminoaciduria, reduced reabsorption of phosphorus, increased excretion of uric acid and carnitine, and decreased serum carnitine, leading to a diagnosis of Fanconi syndrome. 75 g OGTT showed delayed and hyperinsulinemic response similar to that at 38 years old. It is rare for Fanconi syndrome to be associated with insulin-resistant diabetes mellitus despite marked emaciation. The relationship of insulin resistance and carnitine deficiency is discussed.