A novel IGnT allele responsible for the adult i phenotype.
BACKGROUND
The adult i phenotype has been characterized as the presence of a very low level of I antigen but a high quantity of I antigen on red blood cells (RBCs). It has been noted that this rare phenotype is partially associated with congenital cataracts. It has been demonstrated that the human I locus expresses three IGnT forms, IGnTA, IGnTB, and IGnTC, and that the IGnTC gene is responsible for the I antigen expression on RBCs. This report describes molecular genetic analysis of a Taiwanese person with the adult i phenotype but without congenital cataracts.


METHODS
The five exon regions of the IGnT gene of the adult i individual were amplified by polymerase chain reaction (PCR) and cloned, and the sequences were determined. The activity of the IGnT enzyme expressed from the mutant IGnTC gene identified in this i adult was analyzed.


RESULTS
The presented adult i individual possesses wild-type IGnTA and IGnTB genes but a mutant IGnTC gene with a 243T>A nucleotide substitution, which predicts an amino acid alteration of Asn81Lys. PCR-restriction fragment length polymorphism analysis has been used to show that this IGnTC*243A allele is uncommon in the general Taiwanese population. The activity of the IGnT enzyme expressed from the mutant IGnTC*243A gene was significantly reduced when compared with that expressed from the wild-type IGnTC gene.


CONCLUSIONS
A novel IGnTC allele with a 243T>A missense mutation was demonstrated in our adult i Taiwanese without congenital cataracts. The molecular basis revealed for this adult i case agrees with the proposed molecular genetic mechanism, accounting for the partial association of the adult i phenotype with congenital cataracts.
Lin
Marie
M
Transfusion Medicine Laboratory, Mackay Memorial Hospital, Taipei, Taiwan.
Hou
Min-Ju
MJ
Yu
Lung-Chih
LC
D000328:Adult; D000483:Alleles; D019943:Amino Acid Substitution; D044466:Asian People; D002386:Cataract / Q000151:congenital / Q000235:genetics; D005260:Female; D015870:Gene Expression; D006801:Humans; D007048:I Blood-Group System / Q000235:genetics*; D007527:Isoenzymes / Q000235:genetics; D008297:Male; D020125:Mutation, Missense; D017351:N-Acetylglucosaminyltransferases / Q000235:genetics*; D010641:Phenotype; D016133:Polymerase Chain Reaction; D012150:Polymorphism, Restriction Fragment Length; D013624:Taiwan
D007048:I Blood-Group System; D007527:Isoenzymes; C106501:N-acetylglucosaminyltransferase IGnT; D017351:N-Acetylglucosaminyltransferases