Phenotype variability and neonatal diabetes in a large family with heterozygous mutation of the glucokinase gene

Genetic and clinical features of neonatal and early onset diabetes mellitus in a tertiary center cohort in Brazil

Neonatal diabetes mellitus (NDM) is defined as the occurrence of severe hyperglycemia in infants under 6 months old and may be permanent (PNDM) or transient (TNDM). When diabetes is diagnosed at 6-12 months of age (early onset diabetes [EOD]), the etiology may be monogenic; however, most cases consist of type 1 diabetes mellitus (T1DM). Molecular diagnosis was determined in a cohort of 35 unrelated Brazilian patients with NDM or EOD based on targeted next-generation sequencing panel and/or chromosome 6q24 abnormalities. The impact of genetic testing on treatment and follow-up was evaluated. Overall, 24 patients had NDM: with 18 (75.0%) having PNDM, 5 TNDM (20.8%) and 1 case in which this information was unknown. Eleven patients had EOD. Genetic testing was positive in 20/24 patients with NDM (83.3%) and in 18.2% of cases of EOD. The commonest causes were ATP-sensitive potassium (KATP) channel genes, and GCK and IPEX mutations (37.1%, 11.4% and 5.7%, respectively). Patients with PNDM due to KCNJ11 and ABCC8 mutations transitioned successfully to sulfonylureas in almost 60% of cases, reinforcing the benefit of performing genetic testing in NDM as early as possible. This report refers to the largest series of cases of NDM (TNDM and PNDM) and EOD in Brazil in which patients were submitted to molecular investigation and in which the clinical impact of genetic diagnosis was also evaluated.

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.

Monogenic diabetes: a gateway to precision medicine in diabetes

Monogenic diabetes refers to diabetes mellitus (DM) caused by a mutation in a single gene and accounts for approximately 1%-5% of diabetes. Correct diagnosis is clinically critical for certain types of monogenic diabetes, since the appropriate treatment is determined by the etiology of the disease (e.g., oral sulfonylurea treatment of HNF1A/HNF4A-diabetes vs. insulin injections in type 1 diabetes). However, achieving a correct diagnosis requires genetic testing, and the overlapping of the clinical features of monogenic diabetes with those of type 1 and type 2 diabetes has frequently led to misdiagnosis. Improvements in sequencing technology are increasing opportunities to diagnose monogenic diabetes, but challenges remain. In this Review, we describe the types of monogenic diabetes, including common and uncommon types of maturity-onset diabetes of the young, multiple causes of neonatal DM, and syndromic diabetes such as Wolfram syndrome and lipodystrophy. We also review methods of prioritizing patients undergoing genetic testing, and highlight existing challenges facing sequence data interpretation that can be addressed by forming collaborations of expertise and by pooling cases.

Monogenic diabetes prevalence among Polish children-Summary of 11 years-long nationwide genetic screening program

BACKGROUND

Estimated monogenic diabetes (MD) prevalence increases as screening programs proceeds.

OBJECTIVE

To estimate prevalence of MD among Polish children.

SUBJECTS

Patients and their family members suspected of suffering from MD (defined as causative mutation in one of the Maturity Onset Diabetes of the Young or permanent neonatal diabetes mellitus genes) were recruited between January 2005 and December 2015.

METHODS

Nationwide prevalence was estimated based on data from 6 administrative provinces (out of 16 in Poland) with high referral rates of patients (>10 per 100 000 children).

RESULTS

During the analysis, probands from 322 of 788 screened families tested positive yielding a total of 409 children and 299 family members with MD. An average of 70 probands/year were referred. Screening success rate reached 40% over the study period. We estimated the prevalence of MD in 2015 to 7.52/100 000 children (1 in 13 000). The most frequent MODY in this group was GCK- MODY (6.88/100 000). The prevalence estimates increased nearly 2-fold since our report in 2011 (4.4/100 000). However, the figure reached a plateau because of screening saturation in 2014 what was also proven by lowering of the median age of diagnosis lowered in time (R = -0.73, P = .0172) along with shortening of the delay between clinical and genetic diagnosis (R = -0.65, P = .0417).

CONCLUSIONS

The screening for childhood MD in Poland reached a plateau phase after 10 years showing a stable prevalence estimate. The true frequency of MD in the overall population may be higher given later onset of reportedly more frequent types of MD than GCK -MODY.

Familial diabetes of adulthood: A bin of ignorance that needs to be addressed

AIMS

The aim of this article was to share with a wide readership some data and related reasoning about a multigenerational form of diabetes mellitus of adulthood.

DATA SYNTHESIS

We have recently described a familial form of diabetes mellitus, which in the routine clinical setting of adult individuals is simplistically diagnosed as type 2 diabetes. Such misdiagnosis involves as much as 3% of adult unrelated diabetic patients with no evidence of autoimmune disease. More recent data, obtained by means of a next-generation sequencing, indicate that approximately 25% of such patients carry mutations in the genes involved in monogenic diabetes, thus leaving unraveled the molecular causes of the remaining 75% individuals.

CONCLUSIONS

Our proposal is to define the latter patients as being affected by familial diabetes of adulthood (FDA), a clear admission of ignorance and a limbo where adult patients with multigenerational diabetes with no genetic definition of their hyperglycemia have to wait for better times.

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.

A glucokinase gene mutation in a young boy with diabetes mellitus, hyperinsulinemia, and insulin resistance

We report the case of a 12-year-old boy with a glucokinase (GCK) mutation, and diabetes with hyperinsulinemia and insulin resistance. For 4 years, the patient intermittently received insulin medications Actrapid HM and Protaphane HM (total dose 5 U/day), with glycated hemoglobin (HbA_1c) levels of 6.6%–7.0%. After extensive screening the patient was found to carry a heterozygous mutation (p.E256K) in GCK (MIM #138079, reference sequence NM_000162.3). Insulin therapy was replaced by metformin at 1,700 mg/day. One year later, his HbA_1c level was 6.9%, postprandial glycemia at 120 min of oral glucose tolerance test was 15.4 mmol/L, hyperinsulinemia had increased to 508.9 mU/L, homeostasis model assessment index was 114.2 and the Matsuda index was 0.15. Insulin resistance was confirmed by a hyperinsulinemic euglycemic clamp test – M-index was 2.85 mg/kg/min. This observation is a rare case of one of the clinical variants of diabetes, which should be taken into account by a vigilant endocrinologist due to the need for nonstandard diagnostic and therapeutic approaches.

Glycemic variability in patients with Wolfram syndrome is lower than in type 1 diabetes

AIMS

Wolfram syndrome (WFS) is diagnosed as coexistence of diabetes mellitus and optic atrophy, where pancreatic beta cell destruction is associated with neurodegeneration. Typically, WFS necessitates insulin treatment similar to type 1 diabetes (T1D), but the mechanism of beta cell mass reduction leading to hyperglycemia is different.

METHODS

The aim of the study was to assess glycemic variability using the continuous glucose monitoring (CGM) system in seven pediatric patients with genetically confirmed WFS and compare the results with data obtained from 21 propensity score-matched patients with T1D. The "GlyCulator" application was used for the calculation of glycemic variability indices.

RESULTS

CGM recordings showed similarities in glycemic variability among WFS patients, but differing from those of the T1D group. Coefficient of variation (%CV), CONGA4h, and GONGA6h were significantly (p < 0.05) lower in WFS patients (28.08 ± 7.37, 54.96 ± 11.92, and 55.99 ± 10.58) than in T1D patients (37.87 ± 14.24, 74.12 ± 28.74, p = 0.02, and 80.26 ± 35.05, respectively). In WFS patients, the percentage of values above 126 mg/dL was 69.79 (52.08-77.43), whereas in patients with T1D, the percentage was significantly lower-47.22 (35.07-62.85, p = 0.018). Curiously, a tendency toward a lower percentage of measurements below 70 mg/dL was noted in the WFS group [0 (0-7.29)] in comparison with the T1D group [6.25 (0-18.06), p = 0.122]. WFS patients had a significantly higher C-peptide level (0.31 ± 0.2 ng/mL) than T1D patients (0.04 ± 0.04 ng/mL; p = 0.006).

CONCLUSIONS

Patients with WFS show smaller glycemic variability than individuals with T1D, and this may be associated with persistent residual insulin secretion.

Glucokinase gene mutations (MODY 2) in Asian Indians

BACKGROUND AND AIM

Heterozygous inactivating mutations in the glucokinase (GCK) gene cause a hyperglycemic condition termed maturity-onset diabetes of the young (MODY) 2 or GCK-MODY. This is characterized by mild, stable, usually asymptomatic, fasting hyperglycemia that rarely requires pharmacological intervention. The aim of the present study was to screen for GCK gene mutations in Asian Indian subjects with mild hyperglycemia.

SUBJECTS AND METHODS

Of the 1,517 children and adolescents of the population-based ORANGE study in Chennai, India, 49 were found to have hyperglycemia. These children along with the six patients referred to our center with mild hyperglycemia were screened for MODY 2 mutations. The GCK gene was bidirectionally sequenced using BigDye(®) Terminator v3.1 (Applied Biosystems, Foster City, CA) chemistry. In silico predictions of the pathogenicity were carried out using the online tools SIFT, Polyphen-2, and I-Mutant 2.0 software programs.

RESULTS

Direct sequencing of the GCK gene in the patients referred to our Centre revealed one novel mutation, Thr206Ala (c.616A>G), in exon 6 and one previously described mutation, Met251Thr (c.752T>C), in exon 7. In silico analysis predicted the novel mutation to be pathogenic. The highly conserved nature and critical location of the residue Thr206 along with the clinical course suggests that the Thr206Ala is a MODY 2 mutation. However, we did not find any MODY 2 mutations in the 49 children selected from the population-based study. Hence prevalence of GCK mutations in Chennai is <1:1,517.

CONCLUSIONS

This is the first study of MODY 2 mutations from India and confirms the importance of considering GCK gene mutation screening in patients with mild early-onset hyperglycemia who are negative for β-cell antibodies.

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

Mutations in the glucokinase gene (GCK) account for many cases of monogenic diabetes featuring maturity-onset diabetes of the young type 2 (MODY2). The clinical pattern of this form of hyperglycemia is rather stable, with a slight elevation in blood glucose, which is usually not progressive. Patients rarely require pharmacological interventions and microvascular complications related to diabetes are unusual. We describe the clinical follow-up of two cases of MODY2 with two different mutations in GCK gene, one in exon 7, p.Glu265Lys (c.793 G> A), which has been previously described, and a novel one, in exon 2, p.Ser69Stop (c. 206C> G). The clinical course of both cases shows similarity in metabolic control of this form of diabetes over the years.

A SNP in G6PC2 predicts insulin secretion in type 1 diabetes

We investigated whether single nucleotide polymorphisms in genes related to glucose metabolism correlate with insulin secretion in type 1 diabetes patients. A cohort of 49 type 1 diabetes patients underwent serial mixed meal tolerance tests to assess insulin secretion. Patients were genotyped for SNPs related to glucose metabolism: CDKAL1 rs7754840, G6PC2 rs560887, HHEX rs1111875, KCNJ11 rs5215. Recently diagnosed patients (<100 days) homozygous for the G allele of G6PC2 had higher area under the curve C-peptide on mixed meal tolerance tests compared to non-homozygous patients (344.8 ± 203.2 vs. 167.9 ± 131.5, p = 0.04). Other SNPs did not correlate with insulin secretion in the new onset period. In a longitudinal survival analysis, homozygosity for the minor allele (A) in G6PC2 predicted more rapid loss of insulin secretion over time. A SNP in the beta cell gene G6PC2 may correlate with preserved insulin secretion in type 1 diabetes.

The coexistence of type 1 diabetes, MODY2 and metabolic syndrome in a young girl

Even though autoantibodies to pancreatic islet cells are normally found in type 1 diabetes and insulin-resistance due to overweight is more reminiscent of type 2 diabetes, some studies have described β-cell antibodies also in maturity-onset diabetes of the young (MODY) and in type 2 diabetes. A 7-year-old girl was referred to our Unit for incidental hyperglycemia and family history of MODY2 and type 2 diabetes. Genetic evaluation confirmed mutation L134P in exon 4 of the glucokinase gene and a high HLA-risk of type 1 diabetes. During follow-up, she developed type 1 diabetes and overweight-induced metabolic syndrome. The coexistence of MODY, type 1 diabetes and overweight-induced metabolic syndrome confirms that diabetes subtype probably represents a continuum of immune and metabolic dysfunction modified by genetic factors.

Characterization of beta cell and incretin function in patients with MODY1 (HNF4A MODY) and MODY3 (HNF1A MODY) in a Swedish patient collection

The aim of this study was to evaluate the beta cell and incretin function in patients with HNF4A and HNF1A MODY during a test meal. Clinical characteristics and biochemical data (glucose, proinsulin, insulin, C-peptide, GLP-1 and GIP) during a test meal were compared between MODY patients from eight different families. BMI-matched T2D and healthy subjects were used as two separate control groups. The early phase of insulin secretion was attenuated in HNF4A, HNF1A MODY and T2D (AUC0-30 controls: 558.2 ± 101.2, HNF4A MODY: 93.8 ± 57.0, HNF1A MODY: 170.2 ± 64.5, T2D: 211.2 ± 65.3, P < 0.01). Markedly reduced levels of proinsulin were found in HNF4A MODY compared to T2D and that tended to be so also in HNF1A MODY (HNF4A MODY: 3.7 ± 1.2, HNF1A MODY: 8.3 ± 3.8 vs. T2D: 26.6 ± 14.3). Patients with HNF4A MODY had similar total GLP-1 and GIP responses as controls (GLP-1 AUC: (control: 823.9 ± 703.8, T2D: 556.4 ± 698.2, HNF4A MODY: 1,257.0 ± 999.3, HNF1A MODY: 697.1 ± 818.4) but with a different secretion pattern. The AUC insulin during the test meal was strongly correlated with the GIP secretion (Correlation coefficient 1.0, P < 0.001). No such correlation was seen for insulin and GLP-1. Patients with HNF4A and HNF1A MODY showed an attenuated early phase of insulin secretion similar to T2Ds. AUC insulin during the test meal was strongly correlated with GIP secretion, whereas no such correlation was seen for insulin and GLP-1. Thus, GIP may be a more important factor for insulin secretion than GLP-1 in MODY patients.

Functional characterization of MODY2 mutations highlights the importance of the fine-tuning of glucokinase and its role in glucose sensing

Glucokinase (GK) acts as a glucose sensor in the pancreatic beta-cell and regulates insulin secretion. Heterozygous mutations in the human GK-encoding GCK gene that reduce the activity index increase the glucose-stimulated insulin secretion threshold and cause familial, mild fasting hyperglycaemia, also known as Maturity Onset Diabetes of the Young type 2 (MODY2). Here we describe the biochemical characterization of five missense GK mutations: p.Ile130Thr, p.Asp205His, p.Gly223Ser, p.His416Arg and p.Ala449Thr. The enzymatic analysis of the corresponding bacterially expressed GST-GK mutant proteins show that all of them impair the kinetic characteristics of the enzyme. In keeping with their position within the protein, mutations p.Ile130Thr, p.Asp205His, p.Gly223Ser, and p.His416Arg strongly decrease the activity index of GK, affecting to one or more kinetic parameters. In contrast, the p.Ala449Thr mutation, which is located in the allosteric activator site, does not affect significantly the activity index of GK, but dramatically modifies the main kinetic parameters responsible for the function of this enzyme as a glucose sensor. The reduced Kcat of the mutant (3.21±0.28 s(-1) vs 47.86±2.78 s(-1)) is balanced by an increased glucose affinity (S(0.5) = 1.33±0.08 mM vs 7.86±0.09 mM) and loss of cooperativity for this substrate. We further studied the mechanism by which this mutation impaired GK kinetics by measuring the differential effects of several competitive inhibitors and one allosteric activator on the mutant protein. Our results suggest that this mutation alters the equilibrium between the conformational states of glucokinase and highlights the importance of the fine-tuning of GK and its role in glucose sensing.

Neonatal diabetes: an expanding list of genes allows for improved diagnosis and treatment

There has been major progress in recent years uncovering the genetic causes of diabetes presenting in the first year of life. Twenty genes have been identified to date. The most common causes accounting for the majority of cases are mutations in the genes encoding the two subunits of the ATP-sensitive potassium channel (K(ATP)), KCNJ11 and ABCC8, and the insulin gene (INS), as well as abnormalities in chromosome 6q24. Patients with activating mutations in KCNJ11 and ABCC8 can be treated with oral sulfonylureas in lieu of insulin injections. This compelling example of personalized genetic medicine leading to improved glucose regulation and quality of life may-with continued research-be repeated for other forms of neonatal diabetes in the future.