Chronic Mild Hyperglycemia in GCK-MODY Patients Does Not Increase Carotid Intima-Media Thickness

Underestimated risk of secondary complications in pathogenic and glucose-elevating GCK variant carriers with type 2 diabetes

BACKGROUND

Natural HbA1c levels in GCK Maturity-onset diabetes of the young (GCK-MODY) patients often sit above the diagnostic threshold for type 2 diabetes (T2D). Treatments to lower HbA1c levels show reduced effectiveness in these individuals, yet in case studies to date, GCK-MODY patients often evade secondary T2D complications. Given these deviations, genetic screening of GCK may be clinically useful, but population studies are needed to more broadly understand T2D-related complications in GCK variant carriers.

METHODS

To identify GCK variant carriers at the population level, we used both ACMG/AMP variant interpretation for GCK-MODY pathogenicity and a state-of-the-art variant interpretation strategy based on functional and statistical evidence to predict glucose elevations. Presence of pathogenic and glucose-elevating GCK variants was assessed in two cohorts (n~535,000). We identified 442 individuals with GCK variants predicted to increase glucose (~1/1200), with 150 (34%) of these individuals harboring variants reaching a pathogenic interpretation.

RESULTS

In a retrospective analysis, we show that in addition to elevated HbA1c, pathogenic variant carriers are 10x as likely, and all other glucose-elevating GCK variant carriers are 3x as likely, to receive a T2D diagnosis compared to non-GCK carriers. Surprisingly, carriers of pathogenic and glucose-elevating GCK variants with T2D develop T2D-related complications at rates more than double that of individuals without T2D, comparable to non-GCK individuals with T2D.

CONCLUSIONS

This population-level assessment shows secondary complications in individuals with pathogenic and glucose-elevating GCK variants and T2D and suggests that genotyping for these variants should be considered in a precision medicine approach for T2D treatment and prevention.

Identification of pathogenic GCK variants in patients with common type 2 diabetes can lead to discontinuation of pharmacological treatment

Background

Functionally disruptive variants in the glucokinase gene (GCK) cause a form of mild non-progressive hyperglycemia, which does not require pharmacological treatment. A substantial proportion of patients with type 2 diabetes (T2D) carry GCK variants. We aimed to investigate whether carriers of rare GCK variants diagnosed with T2D have a glycemic phenotype and treatment response consistent with GCK-diabetes.

Methods

Eight patients diagnosed with T2D from the Danish DD2 cohort who had previously undergone sequencing of GCK participated. Clinical examinations at baseline included an oral glucose tolerance test and continuous glucose monitoring. Carriers with a glycemic phenotype consistent with GCK-diabetes took part in a three-month treatment withdrawal.

Results

Carriers of pathogenic and likely pathogenic variants had lower median fasting glucose and C-peptide levels compared to carriers of variants of uncertain significance and benign variants (median fasting glucose: 7.3 (interquartile range: 0.4) mmol/l vs. 9.5 (1.6) mmol/l, p = 0.04; median fasting C-peptide 902 (85) pmol/l vs. 1535 (295) pmol/l, p = 0.03). Four participants who discontinued metformin treatment and one diet-treated participant were reevaluated after three months. There was no deterioration of HbA1c or fasting glucose (median baseline HbA1c: 49 (3) vs. 51 (6) mmol/mol after three months, p = 0.4; median baseline fasting glucose: 7.3 (0.4) mmol/l vs. 7.0 (0.6) mmol/l after three months, p = 0.5). Participants did not consistently fulfill best practice guidelines for GCK screening nor clinical criteria for monogenic diabetes.

Discussion

Carriers of pathogenic or likely pathogenic GCK variants identified by unselected screening in T2D should be reported, as they have a glycemic phenotype and treatment response consistent with GCK-diabetes. Variants of uncertain significance should be interpreted with care. Systematic genetic screening of patients with common T2D receiving routine care can lead to the identification and precise care of patients with misclassified GCK-diabetes who are not identifiable through common genetic screening criteria.

Frequency and spectrum of glucokinase mutations in an adult Maltese population

AIM

To investigate the frequency and spectrum of glucokinase (GCK) mutations in a cohort of adults from an island population having a high prevalence of diabetes mellitus (DM).

METHODS

A single-centre cohort study was conducted, including 145 non-obese adults of Maltese-Caucasian ethnicity with impaired fasting glycaemia (IFG) or non-autoimmune diabetes diagnosed before the age of 40 years. Bidirectional sequencing of the GCK coding regions was performed. Genotype-phenotype associations and familial segregation were explored and the effects of missense variants on protein structure were evaluated using computational analysis.

RESULTS

Three probands with pathogenic/likely pathogenic GCK variants in the heterozygous state having clinical features consistent with GCK-diabetes were detected. The missense variants have structurally destabilising effects on protein structure. GCK variant carriers exhibited a significantly lower body mass index and serum triglyceride levels when compared to GCK variant non-carriers.

CONCLUSIONS

The frequency of GCK-diabetes is approximately 2% in non-obese Maltese adults with diabetes or prediabetes. This study broadens the mutational spectrum of GCK and highlights clinical features that could be useful in discriminating GCK-DM from type 2 DM or prediabetes. It reinforces the need for increased molecular testing in young adults with diabetes having a suspected monogenic aetiology.

Cardiovascular risk assessment by coronary artery calcium score in subjects with maturity-onset diabetes of the young caused by glucokinase mutations

AIMS

Maturity-Onset Diabetes of the Young (MODY) caused by glucokinase (GCK) mutations is characterized by lifelong mild non-progressive hyperglycemia, with low frequency of coronary artery disease (CAD) compared to other types of diabetes. The aim of this study is to estimate cardiovascular risk by coronary artery calcification (CAC) score in this group.

MATERIALS AND METHODS

Twenty-nine GCK-MODY cases, 26 normoglycemic controls (recruited among non-affected relatives/spouses of GCK mutation carriers), and 24 unrelated individuals with type 2 diabetes were studied. Patients underwent CAC score evaluation by computed tomography and were classified by Agatston score ≥ or < 10. Framingham Risk scores of CAD in 10 years were calculated.

RESULTS

Median [interquartile range] CAC score in GCK-MODY was 0 [0,0], similar to controls (0 [0,0], P = 0.49), but lower than type 2 diabetes (39 [0, 126], P = 2.6 × 10^-5). A CAC score ≥ 10 was seen in 6.9% of the GCK group, 7.7% of Controls (P = 1.0), and 54.2% of individuals with type 2 diabetes (P = 0.0006). Median Framingham risk score was lower in GCK than type 2 diabetes (3% vs. 13%, P = 4 × 10^-6), but similar to controls (3% vs. 4%, P = 0.66).

CONCLUSIONS

CAC score in GCK-MODY is similar to control individuals from the same family and/or household and is significantly lower than type 2 diabetes. Besides demonstrating low risk of CAD in GCK-MODY, these findings may contribute to understanding the specific effect of hyperglycemia in CAD.

A rare splice site mutation in the gene encoding glucokinase/hexokinase 4 in a patient with MODY type 2

The article presents a variant of maturity onset diabetes of the young type 2, caused by a rare mutation in the GCK gene. Maturity onset diabetes of the young (MODY) is a hereditary form of diabetes with an autosomal dominant type of inheritance, an onset at a young age, and a primary defect in pancreatic β-cell function. This type of diabetes is different from classical types of diabetes mellitus (DM1 and DM2) in its clinical course, treatment strategies, and prognosis. Clinical manifestations of MODY are heterogeneous and may vary even among members of the same family, i. e., carriers of identical mutations. This phenotypic variation is due to the interaction of mutations with different genetic backgrounds and the influence of environmental factors (e. g., lifestyle). Using next-generation sequencing technology, the c.580–1G>A substitution (IVS5 –1G>A, rs1554335421) located in an acceptor splice site of intron 5 of the GCK gene was found in a proband. The identified variant cosegregated with a pathological phenotype in the examined family members. The GCK gene encodes glucokinase (hexokinase 4), which catalyzes the first step in a large number of glucose metabolic pathways such as glycolysis. Mutations in this gene are the cause of MODY2. The illness is characterized by an insignificant increase in the fasting glucose level, is a well-controlled disease without medication, and has a low prevalence of micro- and macrovascular complications of diabetes. The presented case of MODY2 reveals the clinical significance of a mutation in the splice site of the GCK gene. When nonclassical diabetes mellitus is being diagnosed in young people and pregnant women, genetic testing is needed to verify the diagnosis and to select the optimal treatment method. Key words: human; maturity onset diabetes of the young; MODY2; glucokinase gene; next-generation sequencing; genetic analysis; bioinformatics.

How can maturity-onset diabetes of the young be identified among more common diabetes subtypes?

Maturity onset diabetes of the young (MODY) represents a diabetes type which has an enormous clinical impact. It significantly alters treatment, refines a patient's prognosis and enables early detection of diabetes in relatives. Nevertheless, when diabetes is manifested the vast majority of MODY patients are not correctly diagnosed, but mostly falsely included among patients with type 1 or type 2 diabetes, in many cases permanently. The aim of this article is to offer a simple and comprehensible guide for recognizing individuals with MODY hidden among adult patients with another type of long-term diabetes and in women with gestational diabetes.

Novel glucokinase gene mutation in the first Macedonian family tested for MODY

We present a boy with mild hyperglycemia detected during an upper respiratory infection. Novel splicing mutation in the intron 1 of the GCK gene (c.45+1G>A) was detected, and was subsequently confirmed in his father. This is the first case of genetically confirmed Macedonian family with MODY.

The clinical management of hyperglycemia in pregnancy complicated by maturity-onset diabetes of the young

OBJECTIVE

Women with maturity-onset diabetes of the young (MODY) are often first identified and diagnosed with diabetes during pregnancy. Genetics and hyperglycemia play an important role in determining fetal size in MODY pregnancies. The principal objective of the current study is to determine the outcomes and clinical management of hyperglycemia in pregnancies complicated by glucokinase gene (GCK) and hepatocyte nuclear factor (HNF)-1α MODY mutations.

STUDY DESIGN

A retrospective chart review of 37 women with a GCK/HNF-1α mutation was conducted. Data on variables such as birthweight, mode of delivery, and the treatment of hyperglycemia were available on 89 pregnancies.

RESULTS

The birthweight in unaffected GCK offspring was significantly higher than in the affected GCK offspring (4.8 [4.1-5.2] kg vs 3.2 [3.1-3.7] kg; P = .01). Seven-point home blood glucose monitoring over a 7-day period in each trimester demonstrated higher fasting and postprandial glycemic excursions in the first trimester of GCK pregnancies when compared to HNF-1α pregnancies (fasting 104 [90-115] mg/dL vs 84 [77-88] mg/dL; P = .01 and postprandial 154 [135-196] mg/dL vs 111 [100-131] mg/dL; P = .04) despite insulin treatment. There was a higher percentage of miscarriages in the GCK group when compared to the HNF-1α MODY group (33.3% vs 14%; P = .07), which was similar to the background population. Insulin initiated at an early gestation appeared to lower the incidence of macrosomia in GCK unaffected offspring.

CONCLUSION

Hyperglycemia in HNF-1α pregnancies is easily managed with current insulin protocols; in contrast, glycemic excursions are difficult to manage in GCK pregnancies. There was an increased percentage of miscarriages in GCK pregnancies highlighting the importance of a diagnosis of GCK-MODY in women prior to conception and the necessity for preconception care.

Molecular and clinical characterization of glucokinase maturity-onset diabetes of the young (GCK-MODY) in Japanese patients

AIMS

To investigate the molecular and clinical characteristics of the largest series of Japanese patients with glucokinase maturity-onset diabetes of the young (GCK-MODY), and to find any features specific to Asian people.

METHODS

We enrolled 78 Japanese patients with GCK-MODY from 41 families (55 probands diagnosed at the age of 0-14 years and their 23 adult family members). Mutations were identified by direct sequencing or multiplex ligation-dependent probe amplification of all exons of the GCK gene. Detailed clinical and laboratory data were collected on the probands using questionnaires, which were sent to the treating physicians.　Data on current clinical status and HbA1c levels were also collected from adult patients.

RESULTS

A total of 35 different mutations were identified, of which seven were novel. Fasting blood glucose and HbA1c levels of the probands were ≤9.3 mmol/l and ≤56 mmol/mol (7.3%), respectively, and there was considerable variation in their BMI percentiles (0.4-96.2). In total, 25% of the probands had elevated homeostatic assessment of insulin resistance values, and 58.3% of these had evidence of concomitant Type 2 diabetes in their family. The HbA1c levels for adults were slightly higher, up to 61 mmol/mol (7.8%). The incidence of microvascular complications was low. Out of these 78 people with GCK-MODY and 40 additional family members with hyperglycaemia whose genetic status was unknown, only one had diabetic nephropathy.

CONCLUSIONS

The molecular and clinical features of GCK-MODY in Japanese people are similar to those of other ethnic populations; however, making a diagnosis of GCK-MODY was more challenging in patients with signs of insulin resistance.