Multiple miscarriages in two sisters of Thai origin with the rare P^k phenotype caused by a novel nonsense mutation at the B3GALNT1 locus

Objectives: To determine the genetic background underlying the P^k phenotype in two Thai sisters suffering from multiple spontaneous abortions.

Background: The P antigen is carried by globoside, an abundant glycosphingolipid in the red blood cell (RBC) membrane. Inactivating mutations in the 3-β-N-acetylgalactosaminyltransferase gene (B3GALNT1) give rise to the rare P^k phenotype, which lack the P and PX2 antigens. Consequently, naturally occurring anti-P may cause recurrent miscarriages following the cytotoxic attack of the globoside-rich fetal portion of the placenta.

Methods/materials: P/P1/PX2/P^k antigens on RBCs and their corresponding antibodies were detected by haemagglutination and flow cytometry. The B3GALNT1 coding region was sequenced, and an allele-specific polymerase chain reaction (PCR) was developed.

Results: The two sisters had suffered 8 and 11 miscarriages, most of which occurred in the first trimester. Anti-P and anti-PX2 were identified in their plasmas, and the RBCs typed as P-PX2-P^k +, i.e. had the P^k phenotype. Sequencing revealed homozygosity for a nonsense mutation, c.420T>G, in B3GALNT1. This substitution introduces a premature stop codon, p.Tyr140Ter, which is predicted to abolish enzymatic activity. Screening of 384 Thai donors indicated an allele frequency of 0·13%.

Conclusion: We describe a novel nonsense mutation (c.420T>G) in B3GALNT1 (GLOB*01N·13), which was added to the 12 alleles already known in the GLOB system.