caused by has causal or contributing genetic variation Decreased Hemoglobin Concentration Alpha Thalassemia Reduced Hemoglobin A Suggest update to description in HPO. http://purl.obolibrary.org/obo/HP_0011905 Suggest update to description HP:0011905 Hemoglobin A (HbA) contains two alpha-globin chains and two beta-globin chains. HbA is normally the main adult hemoglobin, representing about 96-98 percent of all hemoglobin. This term represents a decrease in the proportion of HbA below this limit, and can be seen in various forms of thalassemia. Beta Thalassemia Mutation Altered Level of Normal Hemoglobin in SCD