[Family Studies of a New Allele of the Bel subtype (c.803G>T, p.Gly268Val)].

Abstract

Objective: To analyze the B_el subtype gene mutation and its genetic mechanism in a family line.

Methods: ABO blood groups were identified by serologic tests. ABO genotyping was performed by polymerase chain reaction with sequence-specific primer (PCR-SSP). Sanger sequencing was performed on exons 1-7 of the ABO gene, the flanking intronic region, and exon 7 of the single strand of the gene confirmed the mutation site location. Missense3D software was used to predict the protein structure alteration caused by this mutation.

Results: Conventional serologic tests failed to detect erythrocyte B antigen in the proband and her three family members, and only trace amounts of B antigen expression could be detected by the absorption-dispersal test. DNA analysis showed that, on the basis of the normal ABO gene, there was a G>T substitution in the position of exon 7, position 803, which resulted in the change of amino acid 268 from Gly to Val. Further single-stranded sequencing analysis showed that the mutation site was located in the B gene.

Conclusion: In this family line, the proband, her father, her son, and her daughter all have reduced B type glycosyltransferase activity due to the new point mutation (c.803G>T) in exon 7 of the B gene, and the B antigen can only be detected by the absorption-dispersal method, and the point mutation can be stably inherited by offspring.