Case report

Rationale: Prader–Willi syndrome (PWS) is a complex genetic disorder that affects multiple systems and results from loss of expression of paternally inherited genes in the 15q11.2–q13 region. It is characterized by severe hypotonia and feeding difficulties during infancy, followed by hyperphagia in later childhood and adolescence, which, without strict control of excessive eating behaviors, ultimately leads to severe obesity associated with type 2 diabetes mellitus. Patient concerns: We present the case of a woman who was diagnosed with PWS and diabetes mellitus in adulthood. She had a history of hypotonia, developmental delay, intellectual disability, hyperphagia, and morbid obesity since childhood, with gonadal dysplasia emerging during puberty. She presented with long-term poorly controlled blood glucose levels. Diagnoses: Genetic testing revealed a heterozygous deletion in the 15q11.2–q13.1 region on chromosome 15, and DNA methylation analysis confirmed the diagnosis of PWS. Interventions: The distinctiveness of this case lies in the patient’s uncontrollable food-seeking behavior combined with PWS-related severe insulin resistance and β-cell dysfunction, which together resulted in refractory diabetes. Initial combination therapy using multiple glucose-lowering agents, including insulin, metformin, chiglitazar sodium, a glucagon-like peptide-1 receptor agonist, and a sodium-glucose cotransporter-2 inhibitor, demonstrated limited efficacy. Outcomes: Subsequent substitution of the glucagon-like peptide-1 receptor agonist with the dual glucose-dependent insulinotropic polypeptide/glucagon-like peptide-1 (GLP-1) receptor agonist tirzepatide led to notable improvements in appetite suppression, body weight reduction, and glycemic control. Lessons: This case underscores the importance of considering genetic syndromes in patients with diabetes presenting with early-onset severe obesity and developmental abnormalities and emphasizes the potential therapeutic value of novel antidiabetic agents such as tirzepatide for managing PWS-associated metabolic disturbances. These findings provide important insights into the diagnosis and treatment of diabetes complicated by PWS.