Abstract: Objective Explore the molecular mechanism of the rare p phenotype in the P1Pk blood group system of the Yi family. Methods Blood groups of the proband and 33 family members were identified by serologic test. Rare blood group genotyping was determined by qRT-PCR, the α-1,4-galactosyltransferase gene and β-1,3-N-acetylgalactosyltransferase were analyzed by Sanger sequencing. Results The proband and his brother are both rare p phenotypes and the serum contains anti-PP1PK antibody that can reacts with all non-p phenotype erythrocytes and causes hemolysis, other pedigree members are the normal P1 or P2 phenotype. The gene sequencing revealed that 2 of the 34 Yi family members were homozygous 456-457 ins ACACCCC (Bank IT: MG812384) in the A4GALT gene coding region, while 6 of them were 456-457ins ACACCCC heterozygous, 7 of them were 109A>G and 987G>A heterozygous, and 3 of them were IVS+228C> T heterozygous. The 7 bp insertion caused the frame shift in reading frame to form a premature termination codon, thus generate an invalid alleles. All the family members showed the consensus B3GALNT1 genes with the standard sequence. Conclusion In Yi family, we identified two cases of p phenotype with a novel A4GALT 456-457 ins ACACCCC alleles. The homozygous mutation is the molecular basis of the p phenotype.

Key words: Yi nationality, P Phenotype, Anti-PP1P^K, A4GALT, New allele, People analysis