H63D syndrome is a serious and clinically progressive disorder of iron metabolism caused by non-transferrin-bound iron (NTBI). In 2019, after scientists from around the world joined together to form the H63D Syndrome Research Consortium (a non-profit entity), a consensus paper "H63D Syndrome" was adopted at a meeting in Oslo in December 2019. With this new paper, we summarize what the leading experts in the field know about the syndrome in 2021.