beta globin gene abnormal beta globin chain HBB gene HBB https://ghr.nlm.nih.gov/gene/HBB "HBB — Hemoglobin, Beta" HBB "HBB — Hemoglobin, Beta" https://ghr.nlm.nih.gov/gene/HBB HBB HBB - hemoglobin, beta - Genetics Home Reference beta US Library of Medicine, 2011