Homozygosity for a novel A4GALT allele resulting in the rare p phenotype in an Indian blood donor.

Background and objectives: Individuals with the rare p phenotype have red cells lacking P, P1 and P^k antigens and make clinically significant anti-PP1P^k. The phenotype arises from inactivating mutations in A4GALT, which encodes the enzyme responsible for production of P1 and P^k. We present results from serological and molecular investigations of a case of anti-PP1P^k with a novel molecular background of the p phenotype.

Materials and methods: Samples from a 32-year-old Indian blood donor were investigated due to the presence of a pan-reactive alloantibody, together with samples from his sister and mother. Standard serological investigations and A4GALT sequencing were performed.

Results: The donor was found to have p phenotype, and his plasma contained anti-PP1P^k. Sequencing revealed a rare homozygous missense mutation in A4GALT (c.526G>A; p.Asp176Asn; rs371893172; frequency 0.00007), representing a novel null allele. The sister was heterozygous for this allele, while surprisingly the mother did not carry the allele. Enquiries revealed the mother was not the donor's biological mother, explaining the perceived discrepant sequencing results.

Conclusion: We have identified homozygosity for a novel A4GALT null allele (carrying c.526G>A, p.Asp176Asn), resulting in lack of functional 4-α-galactosyltransferase and a p phenotype, adding to the catalogue of known genetic backgrounds of this rare phenotype.