The changing landscape of neonatal diabetes mellitus in Italy between 2003-2022

Context: In the last decade Sanger method of DNA sequencing has been replaced by next generation sequencing (NGS). NGS is valuable in conditions characterized by high genetic heterogeneity such as neonatal diabetes mellitus (NDM). Objective: To compare results of genetic analysis of patients with NDM and congenital severe insulin resistance (c.SIR) identified in Italy in 2003-2012 (Sanger) versus 2013-2022 (NGS). Methods: We reviewed clinical and genetic records of 104 cases with diabetes onset before 6 months of age (NDM+c.SIR) of the Italian dataset. Results: Fiftyfive patients (50 NDM + 5 c.SIR) were identified during 2003-2012 and 49 (46 NDM + 3 c.SIR) in 2013-2022. Twenty-year incidence was 1:103,340 (NDM) and 1:1,240,082 (c.SIR) live births. Frequent NDM/c.SIR genetic defects (KCNJ11, INS, ABCC8, 6q24, INSR) were detected in 41 and 34 probands during 2003-2012 and 2013-2022, respectively. We identified a pathogenic variant in rare genes in a single proband (GATA4) (1/42 or 2.4%) during 2003-2012 and in 8 infants (RFX6, PDX1, GATA6, HNF1B, FOXP3, IL2RA, LRBA, BSCL2) during 2013-2022 (8/42 or 19%, p= 0.034 vs 2003-2012). Notably, five among rare genes were recessive. Swift and accurate genetic diagnosis led to appropriate treatment: patients with autoimmune NDM (FOXP3, IL2RA, LRBA), were subjected to bone marrow transplant; patients with pancreas agenesis/hypoplasia (RFX6, PDX1) were supplemented with pancreatic enzymes and the individual with lipodystrophy caused by BSCL2 was started on metreleptin. Conclusions: NGS substantially improved diagnosis and precision therapy of monogenic forms of neonatal diabetes and congenital SIR in Italy.