A male patient with neonatal diabetes and a severe developmental delay at 74 days of life has been described who carries substitutions c.970G>A (p.Val324Met) and Arg1394Leu in the ABCC8 gene; at the age of 6, he still had diabetes (C-peptide level 0.07, HbA1c 61 mmol/mol, and the absence of relevant antibodies), and his treatment was changed to sulfonylureas [38]. The gene discussed is ABCC8; the disease is diabetes mellitus.