Strengths of this study include evaluation of a large cohort of referred adult hemochromatosis probands with HFE p.C282Y homozygosity with HLA-A and -B typing/haplotyping without non-hemochromatosis iron-related disorders or conditions or treatments often associated with abnormal IgG or IgG subclass levels. The gene discussed is HLA-A; the disease is hemochromatosis type 1.