Molecular basis of the adult i phenotype and the gene responsible for the expression of the human blood group I antigen.
The human blood group i and I antigens are characterized as linear and branched repeats of N-acetyllactosamine, respectively. Conversion of the i to the I structure requires the activity of I-branching beta-1,6-N-acetylglucosaminyltransferase (IGnT). Thus the blood group I gene is assigned to encode a beta-1,6-N-acetylglucosaminyltransferase; however, its identity has not been confirmed. The null phenotype of I, the adult i phenotype, provides a means to identify the I gene. Interestingly, the adult i phenotype has been noted to be associated with congenital cataracts in Asians. Molecular genetic studies of 3 adult i pedigrees are reported here. The results obtained on mutation detection within the 2 I-branching enzyme encoding genes, segregation analyses, and enzyme function assays identify molecular changes associated with the adult i phenotype. The adult i phenotype in 2 of the pedigrees studied resulted from 1043G-->A and 1148G-->A mutations, which predict Gly348Glu and Arg383His alterations, respectively, in the IGnT gene. These amino acid changes abolished the original GlcNAc-transferase activity. Deletion of the IGnT gene was observed in the person with adult i phenotype in the third pedigree. These findings suggest that the IGnT gene, first reported in 1993, is the candidate for the blood group I gene. Confirmation of the blood group I gene will further assist in the investigations of the molecular genetics that control I antigen expression in secretions and the molecular basis for the association of the adult i phenotype with congenital cataracts in Asians.
Yu
L C
LC
Transfusion Medicine Laboratory, Department of Medical Research, Mackay Memorial Hospital, Taipei, Taiwan.
Twu
Y C
YC
Chang
C Y
CY
Lin
M
M
D000328:Adult; D001208:Asia; D002386:Cataract / Q000151:congenital / Q000235:genetics; D003001:Cloning, Molecular; D004252:DNA Mutational Analysis; D017353:Gene Deletion; D015870:Gene Expression; D005787:Gene Frequency; D008040:Genetic Linkage; D006801:Humans; D007048:I Blood-Group System / Q000235:genetics*; D008969:Molecular Sequence Data; D009154:Mutation; D020125:Mutation, Missense; D017351:N-Acetylglucosaminyltransferases / Q000235:genetics* / Q000378:metabolism; D010375:Pedigree; D010641:Phenotype; D012150:Polymorphism, Restriction Fragment Length; D020133:Reverse Transcriptase Polymerase Chain Reaction
D007048:I Blood-Group System; C106501:N-acetylglucosaminyltransferase IGnT; D017351:N-Acetylglucosaminyltransferases