Glucokinase Gene Mutations: Structural and Genotype-Phenotype Analyses in MODY Children from South Italy

Abstract

BackgroundMaturity onset diabetes of the young type 2 (or GCK MODY) is a genetic form of diabetes mellitus provoked by mutations in the glucokinase gene (GCK).Methodology/Principal FindingsWe screened the GCK gene by direct sequencing in 30 patients from South Italy with suspected MODY. The mutation-induced structural alterations in the protein were analyzed by molecular modeling. The patients' biochemical, clinical and anamnestic data were obtained. Mutations were detected in 16/30 patients (53%); 9 of the 12 mutations identified were novel (p.Glu70Asp, p.Phe123Leu, p.Asp132Asn, p.His137Asp, p.Gly162Asp, p.Thr168Ala, p.Arg392Ser, p.Glu290X, p.Gln106_Met107delinsLeu) and are in regions involved in structural rearrangements required for catalysis. The prevalence of mutation sites was higher in the small domain (7/12: ∼59%) than in the large (4/12: 33%) domain or in the connection (1/12: 8%) region of the protein. Mild diabetic phenotypes were detected in almost all patients [mean (SD) OGTT = 7.8 mMol/L (1.8)] and mean triglyceride levels were lower in mutated than in unmutated GCK patients (p = 0.04).ConclusionsThe prevalence of GCK MODY is high in southern Italy, and the GCK small domain is a hot spot for MODY mutations. Both the severity of the GCK mutation and the genetic background seem to play a relevant role in the GCK MODY phenotype. Indeed, a partial genotype-phenotype correlation was identified in related patients (3 pairs of siblings) but not in two unrelated children bearing the same mutation. Thus, the molecular approach allows the physician to confirm the diagnosis and to predict severity of the mutation.

Clinical follow-up of two Brazilian subjects with glucokinase-MODY (MODY2) with description of a novel mutation

“…Molecular analysis demonstrated a missense mutation p.Glu265Lys (c.793 G>A) in patient 1, which has already been described in Italian, Spanish, and British populations (22)(23)(24). Previous functional studies demonstrated that this mutation strongly affects protein stability (25).…”

Low prevalence of glucokinase gene mutations in gestational diabetic patients with good glycemic control

“…Primers for amplifying the exons and non-coding exon boundaries 2, 5 + 6 (conjugated), 8, and 9 of the GCK gene have already been described (Tinto et al, 2008). The other primers were designed and analyzed in silico by using the tools Primer3Plus and Blastn.…”

“…*Primers described by Tinto et al (2008). **PCR-SSCP conditions, polyacrylamide (29:1) gel concentration (%) for each amplicon, electrophoresis voltage and run time for BioRad TetraCell (100 x 100-mm plates).…”

“…The human GCK gene is located in the short arm of chromosome 7 (7p15.3-p15.1); it encodes a protein with 465 amino acids (Printz et al, 1993;Gloyn, 2003;Tinto et al, 2008). This gene is about 52 kb long and has 10 exons according to the reference sequence on NCBI (NG_008847.1).…”

“…This gene is about 52 kb long and has 10 exons according to the reference sequence on NCBI (NG_008847.1). Some authors report that the GCK gene might have 12 exons when all mature RNA transcript possibilities are considered (Jetton et al, 1994;Ellard et al, 2000;Gloyn, 2003;Tinto et al, 2008). GCK exon 1 could be described as exon 1a (pancreatic-controlled promoter) and exons 1b/1c as hepatic-controlled promoters (Magnuson and Shelton, 1989;Stoffel et al, 1992).…”