MOLECULAR ANALYSIS OF THE FRUCTOSE TRANSPORTER GENE (GLUT5) IN ISOLATED FRUCTOSE MALABSORPTION

Fructose, a naturally occurring monosaccharide, is increasingly used a s an added sweetener in processed foods in the form of high fructose c orn syrup, Increased fructose intake combined with the identification of children with clinical evidence of isolated fructose malabsorption (IFM) has stimulated interest in possible disorders of fructose absorp tion, The intestinal absorption of fructose is carried out by the faci litative hexose transporter, which has been designated as GLUTS, Funct ional properties and tissue distribution of GLUTS suggest that IFM mig ht be due to mutations in the GLUTS gene. To test this hypothesis, we screened the GLUTS gene for mutations in a group of eight patients wit h IFM and in one subject with global malabsorption, as compared with 1 5 healthy parents of subjects and up to 6 unrelated controls, No mutat ions were found in the protein coding region of this gene in any of th e subjects. A single G to A substitution in the 5' untranslated region of exon 1 was identified in the subject with global malabsorption, Th is subject and her healthy mother were heterozygous for the variant se quence, suggesting that it was unlikely to be clinically significant. In addition, sequence analysis of each of the 12 GLUT5 exons was perfo rmed in the index case and confirmed the negative single-strand confor mation polymorphism findings. These studies demonstrate that IFM does not result from the expression of mutant GLUTS protein.