VDR and hemochromatosis type 1: Previous studies measuring lead blood or bone levels in human populations identified polymorphisms in ALAD encoding δ-aminolevulinic acid dehydratase, associated with heme biosynthesis; VDR, which encodes the vitamin D receptor; and the hemochromatosis-associated gene HFE (Onalaja and Claudio 2000; Warrington et al. 2015; Jhun et al. 2015).