A novel frameshift mutation attributable to 14-nucleotide insertion in hepatocyte nuclearfactor-1 alpha (HNF-1 alpha) encoding a truncated HNF-1 alpha (G554fsX556) with 76-amino acid deletion at its carboxyl terminus was identified in a Thai family with maturity-onset diabetes of the young (MODY). The wild-type and mutant HNF-1 alpha proteins were expressed by in vitro transcription and translation (TNT) assay and by transfection in HeLa cells. The wild-type and mutant HNF-1 alpha could similarly bind to human glucose-transporter 2 (GLUT2) promoter examined by electrophoretic mobility shift assay (EMSA). However, the transactivation activities of mutant HNF-1 alpha on human GLUT2 and rat L-type pyruvate kinase (L-PK) promoters in HeLa cells determined by luciferase reporter assay were reduced to approximately 55-60% of the wild-type protein. These results suggested that the functional defect of novel truncated HNF-1 alpha (G554fsX556) on the transactivation of its target-gene promoters would account for the beta-cell dysfunction associated with the pathogenesis of MODY. (C) 2009 Elsevier Inc. All rights reserved.