Abstract The low-prevalence MNS blood group antigen TSEN is located at the junction of glycophorin A (GPA) to glycophorin B (GPB) in several hybrid glycophorin molecules. Extremely rare people have RBCs with a double dose of the TSEN antigen and have made an antibody to a high-prevalence MNS antigen. We report the first patient who is heterozygous for GYP.JL and M k . During prenatal tests, an alloantibody to a high-prevalence antigen was detected in the serum of a 21-year-old Hispanic woman. The antibody detected an antigen resistant to treatment by papain, trypsin, α-chymotrypsin, or DTT. The antibody was strongly reactive by the IAT with all RBCs tested except those having the M k M k , GP.Hil/GP.Hil, or GP.JL/GP.JL phenotypes. The patient’s RBCs typed M+N–S+/–s–U+, En(a+/–), Hut–, Mi(a–), Mur–, Vw–, Wr(a–b–), and were TSEN+, MINY+. Reactivity with Glycine soja suggested that her RBCs had a decreased level of sialic acid. Immunoblotting showed the presence of monomer and dimer forms of a GP(A-B) hybrid and an absence of GPA and GPB. Sequencing of DNA and PCR-RFLP using the restriction enzyme Rsa I confirmed the presence of a hybrid GYP(A-B) . The patient’s antibody was determined to be anti-En a FR. She is the first person reported with the GP.JL phenotype associated with a deletion of GYPA and GYPB in trans to GYP.JL. Immunohematology 2007;23:146–9.