Variable phenotypic spectrum of diabetes mellitus in a family carrying a novel KCNJ11 gene mutation

Monogenetic Etiologies of Diabetes

Maturity onset diabetes of the young (MODY) describes a group of non-autoimmune forms of diabetes that are characterized by mostly autosomal dominant, monogenic mutations resulting in decreased beta cell function in the pancreas. MODY accounts for roughly 1% to 5% of diabetes cases, and the optimal treatment for each MODY depends on the causative mutation. This article provides a review of MODY to aid providers with knowing what aspects of the history and physical exam should prompt further investigation for this group of conditions.

A novel mutation KCNJ11 R136C caused KCNJ11-MODY

A young female patient, diagnosed with diabetes mellitus at the age of 28 years old in 2009, carries KCNJ11 R136C by whole exome sequencing and her daughter doesn't carry this mutation. Bioinformatics software predicted that the 136th amino acid is highly conservative and the mutation is deleterious. KCNJ11 R136C can result in the change of channel port structure of K_ATP channel. So she was diagnosed as KCNJ11-MODY.

The KCNJ11-E23K Gene Variant Hastens Diabetes Progression by Impairing Glucose-Induced Insulin Secretion

The ATP-sensitive K⁺ (K_ATP) channel controls blood glucose levels by coupling glucose metabolism to insulin secretion in pancreatic β-cells. E23K, a common polymorphism in the pore-forming K_ATP channel subunit (KCNJ11) gene, has been linked to increased risk of type 2 diabetes. Understanding the risk-allele-specific pathogenesis has the potential to improve personalized diabetes treatment, but the underlying mechanism has remained elusive. Using a genetically engineered mouse model, we now show that the K23 variant impairs glucose-induced insulin secretion and increases diabetes risk when combined with a high-fat diet (HFD) and obesity. K_ATP-channels in β-cells with two K23 risk alleles (KK) showed decreased ATP inhibition, and the threshold for glucose-stimulated insulin secretion from KK islets was increased. Consequently, the insulin response to glucose and glycemic control was impaired in KK mice fed a standard diet. On an HFD, the effects of the KK genotype were exacerbated, accelerating diet-induced diabetes progression and causing β-cell failure. We conclude that the K23 variant increases diabetes risk by impairing insulin secretion at threshold glucose levels, thus accelerating loss of β-cell function in the early stages of diabetes progression.

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.

Continuous spectrum of glucose dysmetabolism due to the KCNJ11 gene mutation-Case reports and review of the literature

The KCNJ11 gene encodes the Kir6.2 subunit of the adenosine triphosphate-sensitive potassium (K_ATP ) channel, which plays a key role in insulin secretion. Monogenic diseases caused by KCNJ11 gene mutation are rare and easily misdiagnosed. It has been shown that mutations in the KCNJ11 gene are associated with neonatal diabetes mellitus (NDM), maturity-onset diabetes of the young 13 (MODY13), type 2 diabetes mellitus (T2DM), and hyperinsulinemic hypoglycemia. We report four patients with KCNJ11 gene mutations and provide a systematic review of the literature. A boy with diabetes onset at the age of 1 month was misdiagnosed as type 1 diabetes mellitus (T1DM) for 12 years and received insulin therapy continuously, resulting in poor glycemic control. He was diagnosed as NDM with KCNJ11 E322K gene mutation, and glibenclamide was given to replace exogenous insulin. The successful transfer time was 4 months, much longer than the previous unsuccessful standard of 4 weeks. The other three patients were two sisters and their mother; the younger sister was misdiagnosed with T1DM at 13 years old, while the elder sister was diagnosed with diabetes (type undefined) at 16 years old. They were treated with insulin for 3 years, with poor glycemic control. Their mother was diagnosed with T2DM and achieved good glycemia control with glimepiride. They were diagnosed as MODY13 because of the autosomal dominant inheritance of two generations, early onset of diabetes before 25 years of age in the two sisters, and the presence of the KCNJ11 N48D gene mutation. All patients successfully transferred to sulfonylureas with excellent glycemic control. Therefore, the wide spectrum of clinical phenotypes of glucose dysmetabolism caused by KCNJ11 should be recognized to reduce misdiagnosis and implement appropriate treatment.

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.

KLF11 variant in a family clinically diagnosed with early childhood-onset type 1B diabetes

KLF11 is the causative gene for maturity-onset diabetes of the young 7 (MODY7). KLF11 regulates insulin gene expression through binding to the GC box in the promoter. To date, only two KLF11 mutations have been identified in three families with early-onset type 2 diabetes. Here, we report a novel KLF11 variant associated with early childhood-onset type 1B diabetes. The proband and his younger sister exhibited hyperglycemia at age 1 year, and their mother developed diabetes at age 4 years. These three individuals required insulin injection from the initial phase of the disease. Being negative for islet cell autoantibodies, they were diagnosed with type 1B diabetes. Mutation screening for 30 diabetes-associated genes identified a heterozygous KLF11 variant (p.His418Gln) in the proband and his sister. The variant was also detected in the affected mother, as well as in the allegedly unaffected maternal grandmother. In silico analyses indicated that this variant involves a highly conserved histidine residue in the first C₂ H₂ zinc finger domain which ligates a zinc ion. In vitro analyses showed that expression levels and intracellular localization of His418Gln-KLF11 were comparable to those of wildtype (WT)-KLF11. Luciferase assays demonstrated that while WT-KLF11 suppressed the activity of a 6 × GC box-containing reporter, His418Gln-KLF11 lacked the suppressive effect. Notably, His418Gln-KLF11 canceled the suppressive effect of co-transfected WT-KLF11. Such a dominant-negative effect was absent in the previously reported Ala347Ser-KLF11 variant. These results indicate that specific variants of KLF11 (MODY7) with a dominant-negative effect underlie early childhood-onset type 1B diabetes with incomplete penetrance. This study documents a novel monogenic mutation associated with diabetes in children.

MODY in Siberia – molecular genetics and clinical characteristics

The diagnosis of maturity onset diabetes of the young (MODY) has high clinical significance in young patients (no absolute need for exogenous insulin; normoglycaemia in most patients achieved by dieting or taking oral hypoglycaemic agents) and their relatives (high probability of first-degree relatives being carriers of mutations, which requires a thorough collection of family history and determination of the parameters of carbohydrate metabolism). Aim. This study aimed was to determine the clinical characteristics of different subtypes of MODY in a Siberian region. Materials and Methods. We performed an examination, biochemical and hormonal blood tests, ultrasound and molecular genetic testing of 20 patients with a clinical diagnosis of MODY. Results. Four subtypes of MODY were verified: MODY2 in 11 patients, MODY3 in two, MODY8 in one and MODY12 in two. Eleven patients (69%) exhibited no clinical manifestations of carbohydrate metabolism disorders, and one patient showed weight loss during early stage of the disease. Comorbidities included dyslipidemia, thyroid gland disorders and arterial hypertension. One patient (6%) exhibited diabetic nephropathy; two (13%), diabetic retinopathy and three (19%), peripheral neuropathy of lower legs. All patients achieved the target carbohydrate metabolism; the level of C-peptide was within the reference range. Conclusion. Four different subtypes of MODY (2, 3, 8, 12) were diagnosed in the present study, which differed in their clinical characteristics, presence of complications and treatment strategies. Our knowledge of monogenic forms of diabetes is expanding with the development in molecular genetics, but several aspects related to them require further study.

Neonatal Diabetes and the KATP Channel: From Mutation to Therapy

Activating mutations in one of the two subunits of the ATP-sensitive potassium (K_ATP) channel cause neonatal diabetes (ND). This may be either transient or permanent and, in approximately 20% of patients, is associated with neurodevelopmental delay. In most patients, switching from insulin to oral sulfonylurea therapy improves glycemic control and ameliorates some of the neurological disabilities. Here, we review how K_ATP channel mutations lead to the varied clinical phenotype, how sulfonylureas exert their therapeutic effects, and why their efficacy varies with individual mutations.

Clinical and genetic features of Argentinian children with diabetes-onset before 12months of age: Successful transfer from insulin to oral sulfonylurea

AIMS

Neonatal diabetes mellitus (NDM) is a rare monogenic disorder, reported to affect less than 2 cases per 100,000 infants. There are two types, permanent (PNDM) and transient (TNDM). We describe our clinical experience in determining and comparing the genetic basis of diabetes in children with onset before 6months versus those diagnosed between 6 and 12months of age.

METHODS

We reviewed medical records of children with diabetes diagnosed before 12months of age. Genetic testing was performed in all cases.

RESULTS

12 patients were diagnosed with diabetes before 6months of age (PNDM=6; TNDM=6), and 11 patients between 6 and 12months (all with permanent diabetes). Among children with PNDM, we identified three different KCNJ11 mutations in 5 patients, and one novel ABCC8 mutation in a single patient. Among children with TNDM, we detected a KCNJ11 and ABCC8 mutation each in a single patient and methylation abnormalities at chromosome 6q24 in 4 patients. Among children with diabetes diagnosed between 6 and 12months, 1 patient had an INS mutation and one patient was homozygous for an SLC19A2 mutation which confirmed a diagnosis of thiamine-responsive megaloblastic anaemia syndrome. Five of the patients with an ABCC8 or KCNJ11 mutation have successfully transferred from insulin to glibenclamide whist 1 child demonstrated a partial response to sulfonylurea treatment.

CONCLUSIONS

Investigating the underlying genetic basis of diabetes in children with onset before 1year is useful for choosing the most efficient treatment, the basis of Personalized Medicine.

Neonatal diabetes caused by a homozygous KCNJ11 mutation demonstrates that tiny changes in ATP sensitivity markedly affect diabetes risk

AIMS/HYPOTHESIS

The pancreatic ATP-sensitive potassium (KATP) channel plays a pivotal role in linking beta cell metabolism to insulin secretion. Mutations in KATP channel genes can result in hypo- or hypersecretion of insulin, as in neonatal diabetes mellitus and congenital hyperinsulinism, respectively. To date, all patients affected by neonatal diabetes due to a mutation in the pore-forming subunit of the channel (Kir6.2, KCNJ11) are heterozygous for the mutation. Here, we report the first clinical case of neonatal diabetes caused by a homozygous KCNJ11 mutation.

METHODS

A male patient was diagnosed with diabetes shortly after birth. At 5 months of age, genetic testing revealed he carried a homozygous KCNJ11 mutation, G324R, (Kir6.2-G324R) and he was successfully transferred to sulfonylurea therapy (0.2 mg kg(-1) day(-1)). Neither heterozygous parent was affected. Functional properties of wild-type, heterozygous and homozygous mutant KATP channels were examined after heterologous expression in Xenopus oocytes.

RESULTS

Functional studies indicated that the Kir6.2-G324R mutation reduces the channel ATP sensitivity but that the difference in ATP inhibition between homozygous and heterozygous channels is remarkably small. Nevertheless, the homozygous patient developed neonatal diabetes, whereas the heterozygous parents were, and remain, unaffected. Kir6.2-G324R channels were fully shut by the sulfonylurea tolbutamide, which explains why the patient's diabetes was well controlled by sulfonylurea therapy.

CONCLUSIONS/INTERPRETATION

The data demonstrate that tiny changes in KATP channel activity can alter beta cell electrical activity and insulin secretion sufficiently to cause diabetes. They also aid our understanding of how the Kir6.2-E23K variant predisposes to type 2 diabetes.

Detection of KCNJ11 gene mutations in a family with neonatal diabetes mellitus: implications for therapeutic management of family members with long-standing disease

BACKGROUND

Activating mutations of potassium inwardly-rectifying channel, subfamily J, member 11 (KCNJ11), which encodes Kir6.2 (beta-cell adenosine triphosphate-sensitive potassium [K(ATP)] channel subunit), have been associated with neonatal diabetes mellitus (NDM) in different studies. Treatment with oral sulfonylureas in place of exogenous insulin injections results in improved glycemic control in most patients carrying these mutations. Exploration of genetic causes of NDM occurring before the age of 6 months has been proposed as an important issue in identification of monogenic forms of diabetes, which might be critical in their therapeutic management, as a consequence.

METHODS

Mutation screening of the KCNJ11 gene was carried out using PCR amplification followed by direct sequencing in three family members: the proband, ND1, diagnosed at 40 days of age (current age 7 years); his sibling, ND2, diagnosed at 2 years of age (current age 14 years); and their father, ND3, diagnosed at 15 years of age (current age 35 years), who had been exclusively treated with insulin. The effect of the E227K mutation was also examined in a homology model of Kir6.2.

RESULTS

Our results revealed the presence of the heterozygous missense mutation c. 679 G/A (E227K) in all three patients, who were all able to successfully transfer from insulin injections to an oral sulfonylurea, with improved glycemic control.

CONCLUSION

We found that three members of a family with highly variable age of onset of insulin-treated diabetes, diagnosed at 40 days, 2 years, and 15 years of age, all carried the E227K mutation in KCNJ11 and could switch to an oral sulfonylurea. This mutation has been previously reported in patients with permanent and transient NDM, as well as later-onset diabetes; this report adds to the variability in phenotypic presentation and further supports genetic testing in all diabetic members of any family affected by NDM.

Whole-exome sequencing and high throughput genotyping identified KCNJ11 as the thirteenth MODY gene

Background

Maturity-onset of the young (MODY) is a clinically heterogeneous form of diabetes characterized by an autosomal-dominant mode of inheritance, an onset before the age of 25 years, and a primary defect in the pancreatic beta-cell function. Approximately 30% of MODY families remain genetically unexplained (MODY-X). Here, we aimed to use whole-exome sequencing (WES) in a four-generation MODY-X family to identify a new susceptibility gene for MODY.

Methodology

WES (Agilent-SureSelect capture/Illumina-GAIIx sequencing) was performed in three affected and one non-affected relatives in the MODY-X family. We then performed a high-throughput multiplex genotyping (Illumina-GoldenGate assay) of the putative causal mutations in the whole family and in 406 controls. A linkage analysis was also carried out.

Principal Findings

By focusing on variants of interest (i.e. gains of stop codon, frameshift, non-synonymous and splice-site variants not reported in dbSNP130) present in the three affected relatives and not present in the control, we found 69 mutations. However, as WES was not uniform between samples, a total of 324 mutations had to be assessed in the whole family and in controls. Only one mutation (p.Glu227Lys in KCNJ11) co-segregated with diabetes in the family (with a LOD-score of 3.68). No KCNJ11 mutation was found in 25 other MODY-X unrelated subjects.

Conclusions/Significance

Beyond neonatal diabetes mellitus (NDM), KCNJ11 is also a MODY gene (‘MODY13’), confirming the wide spectrum of diabetes related phenotypes due to mutations in NDM genes (i.e. KCNJ11, ABCC8 and INS). Therefore, the molecular diagnosis of MODY should include KCNJ11 as affected carriers can be ideally treated with oral sulfonylureas.

Current understanding of K ATP channels in neonatal diseases: focus on insulin secretion disorders

ATP-sensitive potassium (K(ATP)) channels are cell metabolic sensors that couple cell metabolic status to electric activity, thus regulating many cellular functions. In pancreatic beta cells, K(ATP) channels modulate insulin secretion in response to fluctuations in plasma glucose level, and play an important role in glucose homeostasis. Recent studies show that gain-of-function and loss-of-function mutations in K(ATP) channel subunits cause neonatal diabetes mellitus and congenital hyperinsulinism respectively. These findings lead to significant changes in the diagnosis and treatment for neonatal insulin secretion disorders. This review describes the physiological and pathophysiological functions of K(ATP) channels in glucose homeostasis, their specific roles in neonatal diabetes mellitus and congenital hyperinsulinism, as well as future perspectives of K(ATP) channels in neonatal diseases.

Unique concurrent appearance of two rare conditions in a young girl: central precocious puberty due to hypothalamic hamartoma and uncommon type of diabetes

Hypothalamic hamartomas (HH) are rare congenital nonneoplastic lesions of the tuber cinereum, which usually present as precocious puberty of central origin in young girls and respond well to treatment with long acting gonadotropin releasing hormone (GnRH) analogs. No association of this condition with diabetes mellitus of any form has been reported so far. On the other hand, diabetes mellitus in children and adolescents, when it is not autoimmune type 1 diabetes, is difficult to classify. We present a girl with early onset of central precocious puberty at the age of 8 months, due to hypothalamic hamartoma. Treatment with depot of a GnRH analog for a period of 9 years and 8 months was successful, and her puberty continued 6 months after the discontinuation of triptorelin. At the age of 9 years 6 months, the girl presented with diabetes. She was negative for islet, GAD and IA2 antibodies and her insulinemia and C-peptide remained within normal limits during the 2 years of follow-up. Her metabolic control is excellent with a combination of metformin and a low-dose of mixed insulin. To our knowledge, this is the first description of the simultaneous appearance of these two endocrinological conditions.

The molecular mechanisms and pharmacotherapy of ATP-sensitive potassium channel gene mutations underlying neonatal diabetes

Neonatal diabetes mellitus (NDM) is a monogenic disorder caused by mutations in genes involved in regulation of insulin secretion from pancreatic β-cells. Mutations in the KCNJ11 and ABCC8 genes, encoding the adenosine triphosphate (ATP)-sensitive potassium (K(ATP)) channel Kir6.2 and SUR1 subunits, respectively, are found in ∼50% of NDM patients. In the pancreatic β-cell, K(ATP) channel activity couples glucose metabolism to insulin secretion via cellular excitability and mutations in either KCNJ11 or ABCC8 genes alter K(ATP) channel activity, leading to faulty insulin secretion. Inactivation mutations decrease K(ATP) channel activity and stimulate excessive insulin secretion, leading to hyperinsulinism of infancy. In direct contrast, activation mutations increase K(ATP) channel activity, resulting in impaired insulin secretion, NDM, and in severe cases, developmental delay and epilepsy. Many NDM patients with KCNJ11 and ABCC8 mutations can be successfully treated with sulfonylureas (SUs) that inhibit the K(ATP) channel, thus replacing the need for daily insulin injections. There is also strong evidence indicating that SU therapy ameliorates some of the neurological defects observed in patients with more severe forms of NDM. This review focuses on the molecular and cellular mechanisms of mutations in the K(ATP) channel that underlie NDM. SU pharmacogenomics is also discussed with respect to evaluating whether patients with certain K(ATP) channel activation mutations can be successfully switched to SU therapy.

Neonatal diabetes mellitus: a model for personalized medicine

Neonatal diabetes mellitus occurs in approximately 1 out of every 100,000 live births. It can be either permanent or transient, and recent studies indicate that is likely to have an underlying genetic cause, particularly when diagnosed before 6 months of age. Permanent neonatal diabetes is most commonly due to activating mutations in either of the genes encoding the two subunits of the ATP-sensitive potassium channel. In most of these patients, switching from insulin to oral sulfonylurea therapy leads to improved metabolic control, as well as possible amelioration of occasional associated neurodevelopmental disabilities. It remains to be determined what is the most appropriate treatment of other causes. The diagnosis and treatment of neonatal diabetes, therefore, represents a model for personalized medicine.

Update in neonatal diabetes

PURPOSE OF REVIEW

Here we give context to new data on neonatal diabetes mellitus, a rare group of insulin-requiring monogenic forms of diabetes presenting at birth or shortly thereafter. Genetic studies are critical in the diagnosis and treatment of these patients. The most common causes of neonatal diabetes are activating mutations in the two protein subunits of the ATP-sensitive potassium channel. These are responsible for about half of all cases of permanent neonatal diabetes and some cases of transient neonatal diabetes. Identification of these mutations allows patients treated with insulin to be transferred to sulfonylureas, but associated conditions and other causes must be considered.

RECENT FINDINGS

Recent data suggest that neonatal diabetes is more common than previously thought, with variable presentations. Continued studies provide further evidence for amelioration of developmental and neurological dysfunction exhibited by a significant proportion of patients. Abnormalities of chromosome 6q24 remain the most common cause of transient neonatal diabetes. Other causes of neonatal diabetes being studied include mutations in proinsulin, FOXP3 mutations in immunodysregulation, polyendocrinopathy, enteropathy, X-linked syndrome, homozygous glucokinase mutations, and Wolcott-Rallinson/EIF2AK3 diabetes.

SUMMARY

We still have much to learn about the different forms of neonatal diabetes, their associated clinical features, and the optimization of therapy using a growing number of available therapeutic agents.