The clinical characterization of six Romanian patients and nine additional patients reported in the literature with JAGN1 deficiency caused by the c.63G>T variant (40% female) revealed a wide phenotypic spectrum, including: neutropenia (all), severe infections (80%), developmental delay (13%), dental problems such as stomatitis/periodontitis (66%), and short stature (7%). The gene discussed is JAGN1; the disease is hyperinsulinemic hypoglycemia, familial, 4.