Galactosemia: deletion in the 5 ' upstream region of the GALT gene reducespromoter efficiency

Galactosemia is a metabolic disorder caused by a defect in the galactose-1- phosphate uridyltransferase (GALT) enzyme. In previous studies, we have sho wn that the presence of a deletion in the 5' upstream (promoter) region of the GALT gene is associated with the Duarte (D2) allele. In the present stu dy, by using a promoter fusion assay we provide direct evidence that a GTCA deletion located in position -119/-116 of the GALT gene (considered in rel ation to the translational start site) decreases transcription of a reporte r gene to about 55% compared with a normal "healthy" promoter transfected i nto human hepatocyte HepG2 cells. This result coincides well with previousl y published biochemical data showing 50% GALT-gene activity in Duarte (D2) galactosemia patients. By transfecting the same promoters (normal and delet ed) into mouse NIH/3T3 cells, we show that the GTCA motif in the promoter r egion of the GALT gene was conserved throughout evolution. We conclude that the -119/-116del-GTCA promoter mutation is a crucial factor in reduction o f Duarte allele enzyme activity.