Three-base deletion and one-base insertion of the alpha(1,4)galactosyltransferase gene responsible for the P phenotype.
Recently, an alpha(1,4)galactosyltransferase gene that is responsible for synthesis of P(k) (Gb3) was isolated. The P individuals who did not express the P(k), P, and P(1) antigens on RBC membranes were shown to lack the P(k) (Gb3) synthase activity because of multiple distinct mutations in the alpha(1,4)galactosyltransferase gene. DNA sequences of the P(k) (Gb3) synthase gene in three Japanese individuals with the p phenotype were analyzed. One individual was found to be homozygous for an allele containing a three-base deletion of CTTCTTC to CTTC from bases 237 through 243 in the coding region. The other two individuals were found to be homozygous for an allele containing a single cytosine insertion in a cytosine repeat at positions 1026 through 1029, resulting in a reading frame shift. The P blood group phenotype is due to several distinct nonfunctional alleles without any predominant allele.