Iron deficiency (ID) is the leading cause of anaemia globally, accounting for 10%–60% of anaemia cases, depending on the population and context (appendix p. 22).35 ID may arise from insufficient iron stores (absolute ID) or limited mobilisation of iron despite adequate stores (functional ID), both impairing haemoglobin production (appendix p. 22).36 Iron is an essential component of haemoglobin and myoglobin, proteins that are involved in oxygen carriage and storage. The gene discussed is MB; the disease is anemia.