Molecular basis of the adult i phenotype and the gene responsible for the expression of the human blood group I antigen

Blood. 2001 Dec 15;98(13):3840-5. doi: 10.1182/blood.v98.13.3840.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Asia
  • Cataract / congenital
  • Cataract / genetics
  • Cloning, Molecular
  • DNA Mutational Analysis
  • Gene Deletion
  • Gene Expression*
  • Gene Frequency
  • Genetic Linkage
  • Humans
  • I Blood-Group System / genetics*
  • Molecular Sequence Data
  • Mutation
  • Mutation, Missense
  • N-Acetylglucosaminyltransferases / genetics*
  • N-Acetylglucosaminyltransferases / metabolism
  • Pedigree
  • Phenotype*
  • Polymorphism, Restriction Fragment Length
  • Reverse Transcriptase Polymerase Chain Reaction


  • I Blood-Group System
  • N-acetylglucosaminyltransferase IGnT
  • N-Acetylglucosaminyltransferases

Associated data

  • GENBANK/AF401652
  • GENBANK/AF401653