CHARACTERIZATION OF A HUMAN GLUTATHIONE-S-TRANSFERASE-MU CLUSTER CONTAINING A DUPLICATED GSTM1 GENE THAT CAUSES ULTRARAPID ENZYME-ACTIVITY

The mu class glutathione S-transferase gene GSTM1 is polymorphic in hu mans, with approximately half of the Caucasian population being homozy gous deleted for this gene. GSTM1 enzyme deficiency has been suggested to predispose people to lung and bladder cancer, Some people in a Sau di Arabian population, however, have been described previously with ul trarapid GSTM1 enzyme activity. Here we have evaluated the molecular g enetic basis for this observation. Genomic DNA from two Saudi Arabian subjects exhibiting ultrarapid enzyme activity and from 13 Swedish sub jects having null, one, or two GSTM1 genes were subjected to restricti on fragment length polymorphism analysis using the restriction enzymes EcoRI, EcoRV, and HindIII and combinations thereof, Hybridization was carried out using a full-length GSTM1 cDNA or the 5' and 3' parts of the cDNA. The restriction mapping data revealed the presence of a GST mu cluster with two GSTM1 genes in tandem situated between the GSTM2 a nd GSTM5 genes. A quantitative multiplex polymerase chain reaction met hod? which simultaneously amplified a fragment of the GSTM1 gene and t he beta-globin gene, was developed, and the genomic GSTM1 copy number was determined from the GSTM1/beta-globin ratio. This method clearly s eparated GSTM1 +/- subjects (ratios between 0.4 and 0.7) from GSTM1 +/ + subjects (ratios between 0.8 and 1.2). The two Saudi Arabians with u ltrarapid GSTM1 activities had ratios of approximately 1.5, indicating that they carried three GSTM1 genes. These results demonstrate the ex istence of a novel mu class GST cluster containing a duplicated active GSTM1 gene causing ultrarapid enzyme activity.