Abnormal Hemoglobin Hemoglobin M http://purl.bioontology.org/ontology/MESH/D006449 Hb M Suggest update to description in MESH (to include "gamma chains") Suggest this term replaces "Methemoglobinemia" below "Abnormal Hemoglobin" in the HPO. Suggest update to description MESH:D006449 HbM Hemoglobin A group of abnormal hemoglobins in which amino acid substitutions take place in either the alpha, beta or gamma chains but near the heme iron. This results in facilitated oxidation of the hemoglobin to yield excess methemoglobin which leads to cyanosis.