Prader-Willi Syndrome with Slowly Progressive Insulin-dependent Diabetes Mellitus.

We report the case of a 52-year-old woman with Prader-Willi syndrome (PWS) and diabetes. Her diabetes was managed with sulfonylurea followed by premixed insulin; however, her glycemic control gradually worsened and became unstable. Her urine and blood C-peptide levels were undetectable. She tested positive for anti-GAD antibodies, and had a high-risk genotype - DRB1*09:01-DQB1*03:03 - for slowly progressive insulin-dependent diabetes mellitus (SPIDDM) in the HLA-DR/DQ region, confirming the diagnosis of SPIDDM. Dysglycemia in PWS is thought to be attributable to hyperphagia and obesity. However, the possibility of SPIDDM might be considered if the insulin secretory capacity is almost lost in patients with PWS.