In the present cohort of 157 hemochromatosis probands, subnormal IgG1, IgG2, IgG3, and IgG4 levels were defined as <3.04 g/L, <1.29 g/L, <0.17 g/L, and <0.01 g/L, respectively. This evidence concerns the gene IGHG3 and hemochromatosis type 1.