Anti-EnaFS detected in the serum of an MiVII homozygote.

Anti-EnaFS was detected in the serum of a Caucasian woman, K.T., during her third pregnancy. She had not been transfused. At delivery, the infant's red cells (RBCs) had a negative direct antiglobulin test. The antibody was inhibited by isolated MN sialoglycoprotein (SGP). Unlike other En(a-) cells, K.T.'s EnaFS-negative RBCs were found to demonstrate normal sialic acid levels, and an MN SGP exhibiting normal sodium dodecylsulphate electrophoretic mobility and periodic acid-Schiff staining intensity. K.T., whose parents were consanguineous, appears to be the first known MiVII homozygote. In a three-generation family study, MiVII was shown to travel with MS. The Anek receptor of K.T.'s RBCs was found to be located on the trypsin-resistant and V8 protease-sensitive portion of the MN SGP (residues 40 to 57), whereas the Anek receptor of MiVI RBCs was shown to be associated with their abnormal Ss SGP. K.T.'s MN SGP appears to exhibit an amino acid sequence alteration in the region of the EnaFS determinant, which is located within the residues 46 to 56 of the normal MN SGP. These findings suggest that the MiVII and EnaFS receptors are the products of allelic genes.