In Alabama and Portugal hemochromatosis patients with HFE p.C282Y homozygosity and positivity for a 500 kb microhaplotype GGG defined by SNPs in chromosome 6p genes PGBD1, ZNF193, and ZNF165 [47], IgG3 levels were significantly higher than those of patients homozygous for microhaplotype AAT that is strongly associated with HLA-A*03 [48]. Here, IGHG3 is linked to hemochromatosis type 1.