In December 2019, the patient was admitted to the endocrinological department of the regional hospital where she was diagnosed with type 1 diabetes mellitus, taking into account the presence of ketonuria +++, levels of glycated hemoglobin (HbA1c) — 7.5% and C-peptide — 0,01 ng/ml (1.1–4.4) and intensified basal-bolus insulin therapy (insulin glargine and aspart) was initiated. The patient was not trained, despite the titration of insulin doses, severe hyperglycemia persisted up to 18.0 mmol/L, and therefore the insulins were changed to degludec and glulisine at the place of residence. This evidence concerns the gene INS and type 1 diabetes mellitus.