ClinVar

Description

The c.781G>C variant in the glucokinase gene, GCK, causes an amino acid change of glycine to arginine at codon 261 (p.(Gly261Arg)) of NM_000162.5. GCK is defined by the ClinGen MDEP as a gene that has a low rate of benign missense variation and has pathogenic missense variants as a common mechanism of disease (PP2). This variant is predicted to be deleterious by computational evidence, with a REVEL score of 0.914, which is greater than the MDEP threshold of 0.70 (PP3). This variant was identified in an individual with a clinical history highly specific for GCK-hyperglycemia (FBG 5.5-8 mmol/L and HbA1c 5.6 - 7.6% and negative antibodies) (PP4_Moderate; internal lab contributors). This variant segregated with hyperglycemia with one informative meioses in a single family; however, this does not meet the thresholds for PP1 set by the ClinGen MDEP (PMID: 27236918, internal lab contributors). This variant was identified in 5 unrelated individuals with hyperglycemia (PS4_Moderate; internal lab contributors). The nucleotide change c.781G>A, which causes the same amino acid change, has been classified as pathogenic by the ClinGen MDEP (PS1). A kinetic analysis of recombinant wild-type (WT) and mutant glucokinase demonstrated that the wild-type kinetic parameters pass the quality control, the wild-type ATP Km is between 0.4-0.65, and the p.Gly261Arg variant has a relative activity index (RAI) of 0.02, which is less than the MDEP VCEP threshold of 0.50 (PMID: 19903754). In summary, the c.781G>C variant meets the criteria to be classified as pathogenic for monogenic diabetes. ACMG/AMP criteria applied, as specified by the ClinGen MDEP VCEP (specification version 1.3.0, approved 8/11/2023): PM2_Supporting, PP2, PP3, PS3_Moderate, PS1, PS4_Moderate, PP4_Moderate.