OBJECTIVE To investigate the frequency of variants of the glucokinase (GCK) gene in subjects with late-onset non-insulin-dependent diabetes mellitus (NIDDM) and in subjects with late-onset impaired glucose tolerance (IGT).

RESEARCH DESIGN AND METHODS The study population included 36 Finnish patients with late-onset NIDDM who were treated with diet for >8 years or who were newly diagnosed and 40 subjects with late-onset IGT who had low or normal insulin levels when tested by an oral glucose tolerance test. All exons, exon-intron junctions, and islet and liver promotor regions of the GCK gene were amplified with the polymerase chain reaction and screened for mutations using single-strand conformation polymorphism analysis.

RESULTS A silent third-base substitution (TAC→TAT) in codon 215 of exon 6 was found in 2.8% of NIDDM patients and in 5.0% of IGT subjects. Polymorphisms were found in islet exon 1 at nucleotide 403 (C→G) in 16.7% of NIDDM patients and in 17.5% of IGT subjects and in the noncoding region of the islet promotor at nucleotide -30 (G→A) in 13.9% of NIDDM patients and in 25.0% of IGT subjects. Furthermore, in liver intron 1 a variant (C→T), 12 base pairs upstream from the splice acceptor site, was found in 5.6% of NIDDM patients and in 7.5% of IGT subjects.

CONCLUSIONS These results indicate that the mutations in the coding region of the GCK gene are not likely to play a major role in the pathogenesis of late-onset NIDDM or IGT in the Finnish population.