A case of isolated hypocalciuric hypercalcemia and type 2 diabetes mellitus followed by Grave\u27s disease

A 73-year-old woman was found to have diabetes mellitus along with elevated levels of calcium and alkaline phosphatase. She had also sometimes exhibited slight elevation of parathyroid hormone (97 pg/ml) while receiving treatment for hypertension and heart failure with atrial fibrillation, which had been detected by the Department of Cardiology at 71 years of age. She was admitted with elevated blood glucose (422 mg/dl) and hemoglobin A1c (12%) levels, as well as for further assessment of hyperparathyroidism. Her diabetes was treated with intensive insulin therapy (insulin lispro at 24 U per day). Assessment of hypercalcemia revealed that urinary calcium excretion was extremely low (0 mg/day) and the fractional excretion of Ca (FECa) was 0%. Familial hypocalciuric hypercalcemia was suspected. No abnormalities of the parathyroid gland were found by ultrasonography and 99mTc+Tl scintigraphy. The patient and her family members did not have any mutations in the extracellular domain or transmembrane domain of the calcium-sensing receptor, which has been reported to play an important role in Ca binding and intracellular signaling. However, the patient did have a missense mutation of codon 990 (R990G) in the intracellular domain, which has been reported to be a site of polymorphism, as well as a mutation of intron 6 (16 base pairs downstream from the exon-intron boundary: IVS6+16). One year later, she developed Grave\u27s disease that presented with fatigue and weight loss