Screening and staging based on islet autoantibody testing and dysglycemia for Type 1 Diabetes (T1D) have become widespread in Western countries. Islet autoantibodies are often detected before the clinical onset of T1D, allowing for the identification of high-risk individuals. By providing appropriate management and intervention before onset, severe complications, such as diabetic ketoacidosis (DKA), can be prevented. Screening studies for individuals with a family history or genetic risk of T1D provide foundational data for early detection and prevention, which could become the basis for strategies to prevent and delay the onset of T1D. This paper outlines the current status of T1D staging and screening in the US and EU, as well as the ongoing activities in Japan.

Diabetes mellitus caused by the insulin (INS) gene has various clinical features. The patient was a 1-year-and-3-month-old girl who manifested symptoms of polydipsia and polyuria. An examination revealed the following: random blood glucose, 265 mg/dL; HbA1c, 14.4 %; islet-related autoantibodies, all negative; and 24-hour urinary C-peptide level, 8 μg/day. The patient was diagnosed with insulin-dependent diabetes mellitus, and continuous subcutaneous insulin infusion was initiated. Her father was diagnosed with diabetes mellitus at 6 months of age and had been receiving intensive insulin therapy since then. Genetic testing revealed a heterozygous missense variant of c.89T>C (p.Leu30Pro) in INS in both the patient and her father. Based on our search, seven pedigrees with variants of the Leu30 residue in the INS gene have been reported. Patients with this Leu30 residue replaced by Arg or Met exhibit the phenotype of maturity-onset diabetes of the young (MODY). Patients with this residue replaced by Gln, Pro, or Val exhibit the phenotype of neonatal diabetes. An accurate diagnosis of monogenic diabetes mellitus is important for selecting appropriate treatment and predicting the patient prognosis.