PNA recognizes the OH-in C4 of Gal in the T-antigen, and ALL recognizes the OH- on C4 and the C-2 acetamido groups of the reduced GalNAc residue of the T-antigenic disaccharide; the former, but not the latter interaction is blocked by the presence of sialic acid at C-3 or C6 (30). The gene discussed is GAL; the disease is acute lymphoblastic leukemia.