To date, seven missense mutations, one nonsense mutation, and two large deletions have been reported; mutations in exon 1C, affecting only the GCNT2C isoform, cause the adult i blood group without cataracts while mutations/deletions affecting exons 2 and 3, shared by all isoforms, result in the adult i blood group along with congenital cataract [7–11]. This evidence concerns the gene GCNT2 and cataract.