INFLUENCE OF LEWIS ALPHA-1-3 4-L-FUCOSYL-TRANSFERASE (FUT3) GENE-MUTATIONS ON ENZYME-ACTIVITY, ERYTHROCYTE PHENOTYPING, AND CIRCULATING TUMOR-MARKER SIALYL-LEWIS A LEVELS/

Fucosylated glycoproteins carrying alpha 1-4 fucose residues are of im portance for cell adhesion and as tumor markers. The Lewis gene, FUT3, encodes the only known alpha 1-4-fucosyltransferase (FucT), and indiv iduals who are deficient in this enzyme type as Lewis-negative on eryt hrocytes. We examined the mutational spectrum of the Lewis gene in Den mark and found 6 different mutations, Five, T59G, T202C, C314T, G508A, and T1067A, were frequent, and one, C445A, was only detected in one o ut of 40 individuals. Allele-specific polymerase chain reaction as web as cloning of FUT3 alleles showed that the 202 and 314 mutations mere co-located on the same allele. COS7 cells transfected with an allele having the 202/314 mutations lacked enzyme activity. Polymerase chain reaction-cleavage assays were established for the genotyping of health y individuals as well as 20 genuine Lewis-negative cancer patients and 10 non-genuine. The latter have Lewis-negative erythrocytes but saliv a alpha 1-4FucT activity. The genuine Lewis-negative individuals had m utations on both FUT3 alleles. In 66 healthy individuals, a gene dosag e effect was detected as FUT3 heterozygous individuals had a lower alp ha 1-4FucT activity in saliva than did homozygous wild-type individual s. The lower enzyme level in heterozygous individuals resulted in a si gnificantly (p < 0.04) lower level of circulating sialyl-Lewis a struc ture in serum. This has the clinical impact that cut-off levels in tum or marker assays should be defined on the basis of genotyping. In the group of non-genuine Lewis-negative cancer patients, whose erythrocyte s convert from Lewis-positive to Lewis-negative during the disease, FU T3 heterozygosity was significantly (p < 0.05) more common.