IGHG3 and hyperinsulinemic hypoglycemia, familial, 4: Importantly, we found that 1-year mortality was highest in patients with IgG1 deficiency (50%), followed by IgG4 deficiency (27.1%), IgG2 deficiency (25.7%), IgG3 deficiency (19.4%), and lowest in those without any IgG subclass deficiencies (16.7%).