ClinVar Genomic variation as it relates to human health

The c.214G>A variant in the glucokinase gene, GCK causes an amino acid change of glycine to arginine at codon 72 (p.(Gly72Arg)) 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 also predicted to be deleterious by computational evidence, with a REVEL score of 0.994, which is greater than the MDEP VCEP threshold of 0.70 (PP3). This variant has an incomputable gnomAD v2.1.1 Popmax minor filtering allele frequency due to 0 copies in the European non-Finnish subpopulation and 1 copies in the African/African American subpopulation, thereby meeting the ClinGen MDEP threshold criteria for PM2_Supporting (ENF Popmax FAF <= 0.000003 and <= 2 copies in ENF and <=1 copy in any other subpopulation) (PM2_Supporting). This variant was identified in 48 unrelated individuals with diabetes/hyperglycemia (PS4; internal lab contributors). 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 OGTT increment < 3 mmol/L) (PP4_Moderate, internal lab contributors). This variant segregated with diabetes/hyperglycemia with 23 informative meioses in multiple families (PP1_Strong; internal lab contributors). A kinetic analysis of recombinant wild-type (WT) and mutant glucokinase demonstrated that the wild-type kinetic parameters passed the quality control, the wild-type ATP Km was between 0.4-0.65, the p.Gly72Arg had a relative activity index (RAI) > 0.5 and a relative stability index (RSI) <=0.5 (PS3_Supporting; PMID: 25015100). In summary, c.214G>A meets the criteria to be classified as Pathogenic for monogenic diabetes. ACMG/AMP criteria applied, as specified by the ClinGen MDEP VCEP (specification version 1.2.0, approved 8/11/2023): PS4, PP1_Strong, PP4_Moderate, PS3_Supporting, PM2_Supporting, PP3, PP2.

The p.Gly72Arg variant substitutes the glycine with arginine at position 72 of the protein. This is a recurrent pathogenic variant that has been reported in the heterozygous state in multiple individuals with MODY (PMID: 19790256, PMID: 10447526, PMID: 12442280, PMID: 30191644 and others). This is not a common variant in the general population (observed in 1 of 251,364 alleles; gnomAD v2.1.1). The p.Gly72Arg variant has been experimentally demonstrated to reduce GCK catalytic activity (PMID: 19187021, PMID: 17389332)

Published functional studies demonstrate increased activity compared to wild type as well as decreased thermal stability of the protein (Sagen et al., 2006; Raimondo et al., 2014); In silico analysis, which includes protein predictors and evolutionary conservation, supports a deleterious effect; Not observed at significant frequency in large population cohorts (gnomAD); Missense variants in this gene are a common cause of disease and they are underrepresented in the general population; This variant is associated with the following publications: (PMID: 17389332, 18399931, 24735133, 29056535, 34462253, 31216263, 21831042, 19187021, 16731834, 25015100, 24411943, 26669242, 12442280, 12955723, 20337973, 17573900, 10447526, 30191644, 30663027, 34108472, 33565752, 34746319)

The p.Gly72Arg variant in GCK has been reported in at least 12 individuals (including 2 Mediterranean, 2 Scandinavian, 2 Spanish, 1 Italian, 1 Czech, 1 Turkish, 1 Slovakian, 1 Norwegian, and 1 Asian individuals) with Monogenic Diabetes, segregated with disease in 6 affected relatives from 3 families (PMID: 27106716, 25015100, 22493702, 18399931, 10447526, 12955723, 20337973, 17573900, 15305805), and has been identified in 0.006155% (1/16248) of African chromosomes by the Genome Aggregation Database (gnomAD, http://gnomad.broadinstitute.org; dbSNP rs193922289). Although this variant has been seen in the general population, its frequency is low enough to be consistent with a carrier frequency. Please note that for diseases with clinical variability, or reduced penetrance, pathogenic variants may be present at a low frequency in the general population. This variant has also been reported pathogenic in ClinVar (Variation ID: 36209). In vitro functional studies provide some evidence that the p.Gly72Arg variant may impact protein activity and interactions with a regulatory protein (PMID: 21831042, 22028181, 17389332, 19187021). However, these types of assays may not accurately represent biological function. Computational prediction tools and conservation analyses suggest that this variant may impact the protein, though this information is not predictive enough to determine pathogenicity. The p.Gly72Arg is located in a region of GCK that is essential to ATP binding and associated with hypoglycemia, suggesting that this variant is in an important functional domain and slightly supports pathogenicity (PMID: 15305805, 19187021). In summary, although additional studies are required to fully establish its clinical significance, this variant is likely pathogenic. ACMG/AMP Criteria applied: PS3_moderate, PS4_Moderate, PP1_Moderate, PM2_Supporting, PP3, PM1_Supporting (Richards 2015).

The GCK p.Gly72Arg variant is pathogenic for maturity-onset diabetes of the young (MODY), with functional studies demonstrating that Gly27Arg results in reduced glucokinase activity and loss of stabilising interactions with glucokinase regulatory protein (PMID: 19187021, 17389332).

Variant summary: GCK c.214G>A (p.Gly72Arg) results in a non-conservative amino acid change located in the Hexokinase, N-terminal domain (IPR022672) of the encoded protein sequence. Five of five in-silico tools predict a damaging effect of the variant on protein function. The variant allele was found at a frequency of 4e-06 in 251464 control chromosomes. c.214G>A has been reported in the literature in multiple individuals affected with Maturity Onset Diabetes Of The Young 2 (example, Mantovani_2003, Lehto_1999, Cao_2002, Pruhova_2010). These data indicate that the variant is very likely to be associated with disease. To our knowledge, no experimental evidence demonstrating an impact on protein function has been reported. Six clinical diagnostic laboratories have submitted clinical-significance assessments for this variant to ClinVar after 2014 without evidence for independent evaluation. All laboratories classified the variant as pathogenic/likely pathogenic. Based on the evidence outlined above, the variant was classified as pathogenic.

This sequence change replaces glycine, which is neutral and non-polar, with arginine, which is basic and polar, at codon 72 of the GCK protein (p.Gly72Arg). This variant is present in population databases (rs193922289, gnomAD 0.007%). This missense change has been observed in individuals with autosomal dominant maturity-onset diabetes of the young (PMID: 10447526, 12442280, 30259503, 30447144, 30663027, 31216263; Invitae). ClinVar contains an entry for this variant (Variation ID: 36209). Advanced modeling of protein sequence and biophysical properties (such as structural, functional, and spatial information, amino acid conservation, physicochemical variation, residue mobility, and thermodynamic stability) performed at Invitae indicates that this missense variant is expected to disrupt GCK protein function. Studies have shown that this missense change alters GCK gene expression (PMID: 16731834, 17389332). This variant disrupts the p.Gly72 amino acid residue in GCK. Other variant(s) that disrupt this residue have been observed in individuals with GCK-related conditions (PMID: 31216263), which suggests that this may be a clinically significant amino acid residue. For these reasons, this variant has been classified as Pathogenic.

The p.G72R variant (also known as c.214G>A), located in coding exon 3 of the GCK gene, results from a G to A substitution at nucleotide position 214. The glycine at codon 72 is replaced by arginine, an amino acid with dissimilar properties. This variant has been identified in numerous maturity onset diabetes of the young families (Lehto M et al. Diabetologia, 1999 Sep;42:1131-7; Cao H et al. Hum. Mutat., 2002 Dec;20:478-9; Mantovani V et al. Hum. Mutat., 2003 Oct;22:338; Sagen JV et al. Pediatr Diabetes, 2008 Oct;9:442-9; Pruhova S et al. Pediatr Diabetes, 2010 Dec;11:529-35; Valent&iacute;nov&aacute; L et al. PLoS ONE, 2012 May;7:e34541; Raimondo A et al. Hum. Mol. Genet., 2014 Dec;23:6432-40; Bansal V et al. BMC Med, 2017 12;15:213). In addition, kinetic studies demonstrated reduced thermal stability compared to wild type (Raimondo A et al. Hum. Mol. Genet., 2014 Dec;23:6432-40). This amino acid position is highly conserved in available vertebrate species. In addition, this alteration is predicted to be deleterious by in silico analysis. Based on the majority of available evidence to date, this variant is likely to be pathogenic.