Phenotypic variability in two siblings with monogenic diabetes due to the same ABCC8 gene mutation

Molecular diagnosis in patients with monogenic diabetes mellitus, and detection of a novel candidate gene

AIM

We aimed to investigate molecular genetic basis of monogenic diabetes (DM) and novel responsible candidate genes with targeted Next Generation Sequencing (NGS) and Whole Exome Sequencing (WES).

METHODS

A hundred cases presenting with clinical findings and a family history of monogenic DM were included in the study. Molecular analysis was performed using an NGS panel including 14 genes. Following targeted NGS, WES was planned in cases in whom no variant was detected.

RESULTS

Thirty different disease-causing variants in seven different genes were detected in thirty-five (35 %) cases with targeted NGS approach. Most common pathogenic variant was found in GCK gene in 25 (25 %) cases. Four different variants were detected in 4 (4 %) patients in ABCC8 gene. In 45 of 65 cases; WES analyses were done. A heterozygous c.2635C > T(p.Gln879Ter) variant was detected in IFIH1 gene in a patient with incidental hyperglycemia. In the segregation analysis affected mother was shown to be heterozygous for the same variant.

CONCLUSION

Molecular etiology was determined in 35 % cases with the NGS targeted panel. Seventeen novel variants in monogenic DM genes have been identified. A candidate gene determined by WES analysis in a case that could not be diagnosed with NGS panel in this study.

ABCC8-related maturity-onset diabetes of the young: switching from insulin to sulphonylurea therapy: how long do we need for a good metabolic control?

OBJECTIVES

Activating variants of the ABCC8 gene cause neonatal diabetes or maturity-onset diabetes of the young (MODY). We report three cases of MODY type 12 caused by variants in the ABCC8 encoding sulphonylurea receptor 1, and the experience of switching from insulin therapy to sulphonylurea therapy.

CASE PRESENTATIONS

We describe a 12.5-year-old girl with permanent neonatal diabetes mellitus, and two diabetes mellitus cases with variants in the ABCC8 gene. Two of these cases were successfully switched from subcutaneous insulin to oral glibenclamide, with a marked improvement in glycemic control. In permanent neonatal diabetes case, glibenclamide dose was progressively increased to achieve a full dose (2 mg/kg/day) in 9 days. Nine months after starting oral sulphonylurea therapy, her blood glucose control dramatically improved and insulin therapy was discontinued.

CONCLUSIONS

We conclude that patients with ABCC8 gene variants can successfully switch from insulin to sulphonylureas.

Role of Actionable Genes in Pursuing a True Approach of Precision Medicine in Monogenic Diabetes

Monogenic diabetes is a genetic disorder caused by one or more variations in a single gene. It encompasses a broad spectrum of heterogeneous conditions, including neonatal diabetes, maturity onset diabetes of the young (MODY) and syndromic diabetes, affecting 1-5% of patients with diabetes. Some of these variants are harbored by genes whose altered function can be tackled by specific actions ("actionable genes"). In suspected patients, molecular diagnosis allows the implementation of effective approaches of precision medicine so as to allow individual interventions aimed to prevent, mitigate or delay clinical outcomes. This review will almost exclusively concentrate on the clinical strategy that can be specifically pursued in carriers of mutations in "actionable genes", including ABCC8, KCNJ11, GCK, HNF1A, HNF4A, HNF1B, PPARG, GATA4 and GATA6. For each of them we will provide a short background on what is known about gene function and dysfunction. Then, we will discuss how the identification of their mutations in individuals with this form of diabetes, can be used in daily clinical practice to implement specific monitoring and treatments. We hope this article will help clinical diabetologists carefully consider who of their patients deserves timely genetic testing for monogenic diabetes.

ABCC8 variants in MODY12: Review of the literature and report of a case with severe complications

More than 1000 variants of the ATP-binding cassette transporter subfamily C member 8 (ABCC8) gene have been reported in neonatal diabetes mellitus. Up to now only 55 ABCC8 variants were associated with Maturity-Onset Diabetes of the Young 12 (MODY12). We present a c.3544C>T p.(Arg1182Trp) ABCC8 variant in a 35-year-old women who had pronounced microvascular diabetic complications and a charcot arthropathy necessitating a lower limb amputation. The unusual severity of the disease course prompted us to perform a systematic review of all genetic variants in MODY12. The present mutation has mostly been associated with neonatal diabetes and in only three papers reporting a MODY12. The 55 MODY12 variants show a large clinical heterogeneity, even in relatives with the same mutation, ranging from mild impaired glucose tolerance to severe insulin-dependent diabetes mellitus. HbA1c at diagnosis ranged from 5% to 14% and age at diagnosis ranged from 2 to 53 years. However, several case reports lack documentation of diabetic complications. Hence, more detailed reports remain necessary to improve insight in MODY12 pathophysiology and outcome. In this article current data regarding therapeutic management are provided, and key points to consider for the individual patient affected by MODY12 are presented.

Molecular mechanisms of β-cell dysfunction and death in monogenic forms of diabetes

Monogenetic forms of diabetes represent 1%-5% of all diabetes cases and are caused by mutations in a single gene. These mutations, that affect genes involved in pancreatic β-cell development, function and survival, or insulin regulation, may be dominant or recessive, inherited or de novo. Most patients with monogenic diabetes are very commonly misdiagnosed as having type 1 or type 2 diabetes. The severity of their symptoms depends on the nature of the mutation, the function of the affected gene and, in some cases, the influence of additional genetic or environmental factors that modulate severity and penetrance. In some patients, diabetes is accompanied by other syndromic features such as deafness, blindness, microcephaly, liver and intestinal defects, among others. The age of diabetes onset may also vary from neonatal until early adulthood manifestations. Since the different mutations result in diverse clinical presentations, patients usually need different treatments that range from just diet and exercise, to the requirement of exogenous insulin or other hypoglycemic drugs, e.g., sulfonylureas or glucagon-like peptide 1 analogs to control their glycemia. As a consequence, awareness and correct diagnosis are crucial for the proper management and treatment of monogenic diabetes patients. In this chapter, we describe mutations causing different monogenic forms of diabetes associated with inadequate pancreas development or impaired β-cell function and survival, and discuss the molecular mechanisms involved in β-cell demise.

Clinical features, complications and treatment of rarer forms of maturity-onset diabetes of the young (MODY) - A review

Maturity onset diabetes of the young (MODY) is the most common form of monogenic diabetes and is currently believed to have 14 subtypes. While much is known about the common subtypes of MODY (MODY-1, 2, 3 and 5) little is known about its rare subtypes (MODY4, 6-14). With the advent of next-generation sequencing (NGS) there are several reports of the rarer subtypes of MODY emerging from across the world. Therefore, a greater understanding on these rarer subtypes is needed. A search strategy was created, and common databases were searched, and 51 articles finally selected. INS-(MODY10) and ABCC8-(MODY12) mutations were reported in relatively large numbers compared to the other rare subtypes. The clinical characteristics of the rare MODY subtypes exhibited heterogeneity between families reported with the same mutation. Obesity and diabetic ketoacidosis (DKA) were also reported among rarer MODY subtypes which presents as a challenge as these are not part of the original description of MODY by Tattersal and Fajans. The treatment modalities of the rarer subtypes included oral drugs, predominantly sulfonylureas, insulin but also diet alone. Newer drugs like DPP-4 and SGLT2 inhibitors have also been tried as new modes of treatment. The microvascular and macrovascular complications among the patients with various MODY subtypes are less commonly reported. Recently, there is a view that not all the 14 forms of 'MODY' are true MODY and the very existence of some of these rarer subtypes as MODY has been questioned. This scoping review aims to report on the clinical characteristics, treatment and complications of the rarer MODY subtypes published in the literature.

Clinical and Genetic Characteristics of ABCC8 Nonneonatal Diabetes Mellitus: A Systematic Review

OBJECTIVES

Diabetes mellitus (DM) is a major chronic metabolic disease in the world, and the prevalence has been increasing rapidly in recent years. The channel of K_ATP plays an important role in the regulation of insulin secretion. The variants in ABCC8 gene encoding the SUR1 subunit of K_ATP could cause a variety of phenotypes, including neonatal diabetes mellitus (ABCC8-NDM) and ABCC8-induced nonneonatal diabetes mellitus (ABCC8-NNDM). Since the features of ABCC8-NNDM have not been elucidated, this study is aimed at concluding the genetic features and clinical characteristics.

METHODS

We comprehensively reviewed the literature associated with ABCC8-NNDM in the following databases: MEDLINE, PubMed, and Web of Science to investigate the features of ABCC8-NNDM.

RESULTS

Based on a comprehensive literature search, we found that 87 probands with ABCC8-NNDM carried 71 ABCC8 genetic variant alleles, 24% of whom carried inactivating variants, 24% carried activating variants, and the remaining 52% carried activating or inactivating variants. Nine of these variants were confirmed to be activating or inactivating through functional studies, while four variants (p.R370S, p.E1506K, p.R1418H, and p.R1420H) were confirmed to be inactivating. The phenotypes of ABCC8-NNDM were variable and could also present with early hyperinsulinemia followed by reduced insulin secretion, progressing to diabetes later. They had a relatively high risk of microvascular complications and low prevalence of nervous disease, which is different from ABCC8-NDM.

CONCLUSIONS

Genetic testing is essential for proper diagnosis and appropriate treatment for patients with ABCC8-NNDM. And further studies are required to determine the complex mechanism of the variants of ABCC8-NNDM.

New insights into KATP channel gene mutations and neonatal diabetes mellitus

The ATP-sensitive potassium channel (K_ATP channel) couples blood levels of glucose to insulin secretion from pancreatic β-cells. K_ATP channel closure triggers a cascade of events that results in insulin release. Metabolically generated changes in the intracellular concentrations of adenosine nucleotides are integral to this regulation, with ATP and ADP closing the channel and MgATP and MgADP increasing channel activity. Activating mutations in the genes encoding either of the two types of K_ATP channel subunit (Kir6.2 and SUR1) result in neonatal diabetes mellitus, whereas loss-of-function mutations cause hyperinsulinaemic hypoglycaemia of infancy. Sulfonylurea and glinide drugs, which bind to SUR1, close the channel through a pathway independent of ATP and are now the primary therapy for neonatal diabetes mellitus caused by mutations in the genes encoding K_ATP channel subunits. Insight into the molecular details of drug and nucleotide regulation of channel activity has been illuminated by cryo-electron microscopy structures that reveal the atomic-level organization of the K_ATP channel complex. Here we review how these structures aid our understanding of how the various mutations in the genes encoding Kir6.2 (KCNJ11) and SUR1 (ABCC8) lead to a reduction in ATP inhibition and thereby neonatal diabetes mellitus. We also provide an update on known mutations and sulfonylurea therapy in neonatal diabetes mellitus.

Phenotype, genotype and glycaemic variability in people with activating mutations in the ABCC8 gene: response to appropriate therapy

AIMS

To examine the phenotypic features of people identified with ABCC8-maturity-onset diabetes of the young (MODY) who were included in the adult 'Mater MODY' cohort and to establish their response to sulfonylurea therapy.

METHODS

Ten participants with activating ABCC8 mutations were phenotyped in detail. A 2-hour oral glucose tolerance test was performed to establish glycaemic tolerance, with glucose, insulin and C-peptide measurements taken at baseline and 30-min intervals. Insulin was discontinued and sulfonylurea therapy initiated after genetic diagnosis of ABCC8-MODY. A blinded continuous glucose monitoring sensor was used to establish glycaemic control on insulin vs a sulfonylurea.

RESULTS

The mean age at diagnosis of diabetes was 33.8 ± 11.1 years, with fasting glucose of 18.9 ± 11.5 mmol/l and a mean (range) HbA_1c of 86 (51,126) mmol/mol [10.0 (6.8,13.7)%]. Following a genetic diagnosis of ABCC8-MODY three out of four participants discontinued insulin (mean duration 10.6 ± 1.69 years) and started sulfonylurea treatment. The mean (range) HbA_1c prior to genetic diagnosis was 52 (43,74) mmol/mol (6.9%) and the post-treatment change was 44 (30,57) mmol/mol (6.2%; P=0.16). Retinopathy was the most common microvascular complication in this cohort, occurring in five out of 10 participants.

CONCLUSIONS

Low-dose sulfonylurea therapy resulted in stable glycaemic control and the elimination of hypoglycaemic episodes attributable to insulin therapy. The use of appropriate therapy at the early stages of diabetes may decrease the incidence of complications and reduce the risks of hypoglycaemia associated with insulin therapy.