Even though autoantibodies to pancreatic islet cells are normally found in type 1 diabetes and insulin-resistance due to overweight is more reminiscent of type 2 diabetes, some studies have described β-cell antibodies also in maturity-onset diabetes of the young (MODY) and in type 2 diabetes. A 7-year-old girl was referred to our Unit for incidental hyperglycemia and family history of MODY2 and type 2 diabetes. Genetic evaluation confirmed mutation L134P in exon 4 of the glucokinase gene and a high HLA-risk of type 1 diabetes. During follow-up, she developed type 1 diabetes and overweight-induced metabolic syndrome. The coexistence of MODY, type 1 diabetes and overweight-induced metabolic syndrome confirms that diabetes subtype probably represents a continuum of immune and metabolic dysfunction modified by genetic factors.