A novel cis-AB allele derived from a unique 796C>A mutation in exon 7 of ABO gene.
BACKGROUND
The cis-AB phenotype is very rare, and only three genotypes that correspond to specific ABO allele changes have been reported. Cis-AB01 involves the A102 allele with a nonsynonymous substitution G803C in exon 7, whereas cis-AB02 and cis-AB03 involve different nonsynonymous substitutions A796C and C700T, respectively, on the B101 allele background. The nucleotide substitutions give rise to a change of the respective glycosyltransferase, resulting in varying bifunctional AB transferase activities.


METHODS
Two cis-AB phenotypes were identified in a Taiwanese C. family and two unrelated individuals, respectively. Serologic studies, molecular cloning, and sequencing of exon 6 and exon 7 were carried out to determine their respective phenotypic characteristics and cis-AB alleles. A cohort of 300 AB-phenotype, healthy random individuals served as controls.


RESULTS
A novel cis-AB allele is uncovered out of the three family members, of which a 796C>A substitution occurs predicting an amino acid change at residue 266 of leucine to methionine on the background of A102 allele. It is serologically like cis-AB03, an A2B phenotype, but molecularly different. Both of the two unrelated individuals are of cis-AB01 allele, and all of the 300 AB blood group controls are excluded cis-AB phenotype.


CONCLUSIONS
The C. family described carries a novel cis-AB allele that differs molecularly from all previously reported cis-AB alleles.
Tzeng
Cheng-Hwai
CH
Section of Transfusion Medicine, Department of Medicine, Veterans General Hospital; and the College of Medicine, National Yang-Ming University, Taipei, Taiwan. chtzeng@vghtpe.gov.tw
Chen
Ying-Ju
YJ
Lyou
Jau-Yi
JY
Chen
Pei-Shan
PS
Liu
Hsueng-Mei
HM
Hu
Hui-Yu
HY
Lin
Jeong-Shi
JS
Yu
Lung-Chih
LC
D000017:ABO Blood-Group System / Q000235:genetics*; D000483:Alleles; D005091:Exons; D005260:Female; D006801:Humans; D009154:Mutation
D000017:ABO Blood-Group System