Population-based estimates for double diabetes amongst people with glucokinase monogenic diabetes, GCK-MODY

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.

How do I diagnose Maturity Onset Diabetes of the Young in my patients?

Maturity Onset Diabetes of the Young (MODY) is a monogenic form of diabetes diagnosed in young individuals that lack the typical features of type 1 and type 2 diabetes. The genetic subtype of MODY determines the most effective treatment and this is the driver for MODY genetic testing in diabetes populations. Despite the obvious clinical and health economic benefits, MODY is significantly underdiagnosed with the majority of patients being inappropriately managed as having type 1 or type 2 diabetes. Low detection rates result from the difficulty in identifying patients with a likely diagnosis of MODY from the high background population of young onset type 1 and type 2 diabetes, compounded by the lack of MODY awareness and education in diabetes care physicians. MODY diagnosis can be improved through (1) access to education and training, (2) the use of sensitive and specific selection criteria based on accurate prediction models and biomarkers to identify patients for testing, (3) the development and mainstream implementation of simple criteria-based selection pathways applicable across a range of healthcare settings and ethnicities to select the most appropriate patients for genetic testing and (4) the correct use of next generation sequencing technology to provide accurate and comprehensive testing of all known MODY and monogenic diabetes genes. The creation and public sharing of educational materials, clinical and scientific best practice guidelines and genetic variants will help identify the missing patients so they can benefit from the more effective clinical care that a genetic diagnosis brings.

Maturity onset diabetes of the young type 2 (MODY2): Insight from an extended family

AIMS

To assess long-term outcome of patients with maturity onset diabetes of the young, type 2 (MODY2) in a unique large cohort of patients with the same genetic and environmental background.

METHODS

We prospectively evaluated 162 patients aged 5 to 82 years, belonging to the same extended family living in the same village. All patients underwent molecular testing for the glucokinase (GCK) gene mutation identified in the proband, and were categorized into three groups (MODY2, type 2 diabetes and controls).

RESULTS

The 5.5-year-old proband had the c.1278_1286del mutation in the GCK and was diagnosed with MODY2. Forty-two out of 162 participants were positive for the mutation and 39 had type 2 diabetes. Patients were followed for a mean 10.2 ± 3.7 years (range 0-14). Mean fasting blood glucose and HbA1c increased significantly over the years in MODY2 patients (133 vs. 146 mg/dL; 6.9% vs. 8.2%, respectively). Increase in HbA1c occurred only in the obese/overweight subgroups. Twenty-five percent of MODY2 patients developed diabetes complications, all were above 40 years of age.

CONCLUSIONS

Although MODY2 commonly has a benign disease course, weight gain is a risk factor for diabetes complications, requiring life-long follow-up and in some patients, medical intervention.

Atypical diabetes: a diagnostic challenge

In medical school, we learned how to classify diabetes according to different clinical characteristics. However, at the dawn of the precision medicine era, it is clear that today's clinical reality does not always align well with textbook teachings. The terms juvenile versus elderly-onset diabetes, as well as insulin-dependent versus non-insulin-dependent diabetes, have become obsolete. Contrary to what is often taught severe ketoacidosis may occur in type 2 diabetes. Patients may also suffer from two or more forms of diabetes simultaneously or consecutively. Five authentic cases of diabetes with uncommon characteristics that pose diagnostic challenges are presented here.

Update on clinical screening of maturity-onset diabetes of the young (MODY)

BACKGROUND

Maturity-onset diabetes of the young (MODY) is the most common type of monogenic diabetes, being characterized by beta-cell disfunction, early onset, and autosomal dominant inheritance. Despite the rapid evolution of molecular diagnosis methods, many MODY cases are misdiagnosed as type 1 or type 2 diabetes. High costs of genetic testing and limited knowledge of MODY as a relevant clinical entity are some of the obstacles that hinder correct MODY diagnosis and treatment. We present a broad review of clinical syndromes related to most common MODY subtypes, emphasizing the role of biomarkers that can help improving the accuracy of clinical selection of candidates for molecular diagnosis.

MAIN BODY

To date, MODY-related mutations have been reported in at least 14 different genes. Mutations in glucokinase (GCK), hepatocyte nuclear factor-1 homeobox A (HNF1A), and hepatocyte nuclear factor-4 homeobox A (HNF4A) are the most common causes of MODY. Accurate etiological diagnosis can be challenging. Many biomarkers such as apolipoprotein-M (ApoM), aminoaciduria, complement components, and glycosuria have been tested, but have not translated into helpful diagnostic tools. High-sensitivity C-reactive protein (hs-CRP) levels are lower in HNF1A-MODY and have been tested in some studies to discriminate HNF1A-MODY from other types of diabetes, although more data are needed. Overall, presence of pancreatic residual function and absence of islet autoimmunity seem the most promising clinical instruments to select patients for further investigation.

CONCLUSIONS

The selection of diabetic patients for genetic testing is an ongoing challenge. Metabolic profiling, diabetes onset age, pancreatic antibodies, and C-peptide seem to be useful tools to better select patients for genetic testing. Further studies are needed to define cut-off values in different populations.

Hexokinase Domain Containing 1 (HKDC1) Gene Variants and their Association with Gestational Diabetes Mellitus in a South Indian Population

Hexokinase domain containing 1 (HKDC1), a novel human hexokinase gene, is known to affect glucose metabolism and was shown to have a strong association with 2-h plasma glucose in pregnant women in a recent genome wide association study. This study aimed to evaluate the association of these regulatory variants of HKDC1 (rs1076224, rs4746822, rs2394529 and rs9645501) with gestational diabetes mellitus (GDM) in a South Indian population. The regulatory variants of HKDC1 were genotyped in unrelated 500 women with GDM and 510 non-GDM individuals by using the MassARRAY system and by direct DNA sequencing. The minor alleles of the HKDC1 gene regulatory variants, namely rs10762264 and rs4746822, showed a significant association with GDM and these alleles conferred as much as 1.24 and 1.34 times higher risk for GDM, respectively. This is the first study to demonstrate the association of HKDC1 genetic variants with susceptibility to GDM.

Coordinated regulatory variation associated with gestational hyperglycaemia regulates expression of the novel hexokinase HKDC1

Maternal glucose levels during pregnancy impact the developing fetus, affecting metabolic health early and later in life. Both genetic and environmental factors influence maternal metabolism, but little is known about the genetic mechanisms that alter glucose metabolism during pregnancy. Here we report that haplotypes previously associated with gestational hyperglycemia in the third trimester disrupt regulatory element activity and reduce expression of the nearby HKDC1 gene. We further find that experimentally reducing or increasing HKDC1 expression reduces or increases hexokinase activity, respectively, in multiple cellular models; and that purified HKDC1 protein has hexokinase activity in vitro. Together, these results suggest a novel mechanism of gestational glucose regulation in which the effects of genetic variants in multiple regulatory elements alter glucose homeostasis by coordinately reducing expression of the novel hexokinase HKDC1.