Individuals could be classified as 'secretors' and 'nonsecretors'according to their ability to secrete ABO blood group antigens in saliva  ABO blood group antigens (A, B, and H), in addition to their presence on blood cells and platelets, are also present on other tissue cells and are variably expressed through body fluids, such as saliva, tears, semen, urine, gastric juice, and breast milk, depending on whether the individual possesses the secretor gene or not, the inherited A, B, O genes,and Lewis blood group system 
The secretor gene encodes for enzymes (glycosyltransferases), which become activein mucin-secreting cells like goblet and mucous cells of mucous membranes and different glands, resulting in the secretion of the corresponding blood group antigens in the body fluids .
5ABH secretions are controlled by fucosyletransferase 2 (FUT2) secretor gene
located on the short arm of chromosome number 19 in the form of two alleles denoted as Se" and se".
Two independent genes determine the Lewis phenotype; the Lewis gene (Le and le), and the secretor gene (Se and se; Fig.
Recently, the Lewis gene (FUT3) and the secretor gene (FUT2) were cloned (2, 3), and several silent alleles that cause the Lewis-negative (4-9) and the nonsecretor (1015) phenotypes, respectively, were identified.
As expected, individuals who were heterozygous mutated in the secretor gene (genotype groups 3 and 4) had higher concentrations of CA 19-9 in serum than individuals who were homozygous wild type (genotype groups 5 and 6; borderline significant for individuals who were homozygous wild type in the Lewis gene: P = 0.
Secretor gene inactivation by a novel single missense mutation A358T in Japanese nonsecretor individuals.
Lewis and secretor gene dosages affect CA 19-9 and DU-PAN-2 serum levels in normal individuals and colorectal cancer patients.
6 Genotype groups Lewis gene Secretor gene 1 Le/Le se/se 51 14.
The recent cloning of the secretor gene (FUT2) and the identification of enzyme-inactivating mutations and gene fusion [25-30] may even make it possible to classify the secretors as homozygous wild-type and heterozygous at the FUT2 locus, once the geographical distribution of inactivating mutations has been documented.
The synthesis of Ca 19-9 is complex because there are three genes involved: the secretor gene, the gene encoding the sialyltransferase, and the Lewis gene.
The dosage of the Lewis gene [fucosyltransferase 3 (galactoside 3(4)-L-fucosyltransferase, Lewis blood group)] increases the amount of CA 19-9, whereas the dosage of secretor genes
decreases it (6).