Type 1 Diabetes Mellitus in a Child With Genetically Confirmed Alström Syndrome: An Unusual Autoimmune Phenotype.

Alström syndrome (AS) is a rare autosomal recessive multisystem disorder caused by pathogenic variants in the ALMS1 gene and is classically associated with obesity, insulin resistance, and type 2 diabetes mellitus (T2DM). We report a 9-year-and-10-month-old girl with genetically confirmed Alström syndrome who developed diabetes mellitus at 5 years of age. Unlike the typical metabolic phenotype reported in Alström syndrome, the patient demonstrated positive anti-glutamic acid decarboxylase (GAD) and insulinoma-associated antigen-2 (IA-2) antibodies, progressive decline in endogenous insulin secretion, and persistent insulin dependence, consistent with autoimmune type 1 diabetes mellitus (T1DM). Despite obesity, there were no significant clinical features of severe insulin resistance. Glycemic control progressively deteriorated over follow-up despite intensive insulin therapy. This case highlights the phenotypic variability of diabetes in Alström syndrome and emphasizes the importance of comprehensive endocrine evaluation to ensure accurate diabetes classification and appropriate management.