Molecular basis of the globoside-deficient Pk blood group phenotype -: Identification of four inactivating mutations in the UDP-N-acetylgalactosamine:: Globotriaosylceramide 3-β-N-acetylgalactosaminyltransferase gene

The biochemistry and molecular genetics underlying the related carbohydrate blood group antigens P, P-k, and LKE in the GLOB collection and P1 in the P blood group system are complex and not fully understood. Individuals with the rare but clinically important erythrocyte phenotypes P-1(k) and P-2(k) lack the capability to synthesize P antigen identified as globoside, the cellular receptor for Parvo-B19 virus and some P-fimbriated Escherichia coli. As in the ABO system, naturally occurring antibodies, anti-P of the IgM and IgG class with hemolytic and cytotoxic capacity, are formed. To define the molecular basis of the P-k phenotype we analyzed the full coding region of a candidate gene reported in 1998 as a member of the 3-beta-galactosyltransferase family but later shown to possess UDP-N-acetylgalactosamine:globotriaosylceramide 3-beta-N-acetylgalactosaminyltransferase or globoside synthase activity. Homozygosity for different nonsense mutations (C-202 --> T and 538insA) resulting in premature stop codons was found in blood samples from two individuals of the P-2(k) phenotype. Two individuals with P-1(k) and P-2(k) phenotypes were homozygous for missense mutations causing amino acid substitutions (E266A or G271R) in a highly conserved region of the enzymatically active carboxyl-terminal domain in the transferase. We conclude that crucial mutations in the globoside synthase gene cause the P-k phenotype.