KATP channel mutation disrupts hippocampal network activity and nocturnal gamma shifts.

ATP-sensitive potassium (KATP) channels couple cell metabolism to cellular electrical activity. Humans affected by severe activating mutations in KATP channels suffer from developmental delay, epilepsy, and neonatal diabetes (DEND syndrome). While the aetiology of diabetes in DEND syndrome is well understood, the pathophysiology of the neurological symptoms remains unclear. We hypothesised that impaired activity of parvalbumin-positive interneurons (PV-INs) may result in seizures and cognitive problems. We found, by performing electrophysiological experiments, that expressing the DEND mutation Kir6.2-V59M selectively in mouse PV-INs reduced intrinsic gamma frequency preference and short-term depression as well as disturbed cognition-associated gamma oscillations and hippocampal sharp waves. Furthermore, the risk of seizures was increased and the day-night shift in gamma activity disrupted. Blocking KATP channels with tolbutamide partially rescued the network oscillations. The non-reversible part may, to some extent, result from observed altered PV-IN dendritic branching and PV-IN arrangement within CA1. In summary, PV-INs play a key role in DEND syndrome, and this provides a framework for establishing treatment options.

Cognitive deficits and impaired hippocampal long-term potentiation in KATP-induced DEND syndrome.

ATP-sensitive potassium (KATP) gain-of-function (GOF) mutations cause neonatal diabetes, with some individuals exhibiting developmental delay, epilepsy, and neonatal diabetes (DEND) syndrome. Mice expressing KATP-GOF mutations pan-neuronally (nKATP-GOF) demonstrated sensorimotor and cognitive deficits, whereas hippocampus-specific hKATP-GOF mice exhibited mostly learning and memory deficiencies. Both nKATP-GOF and hKATP-GOF mice showed altered neuronal excitability and reduced hippocampal long-term potentiation (LTP). Sulfonylurea therapy, which inhibits KATP, mildly improved sensorimotor but not cognitive deficits in KATP-GOF mice. Mice expressing KATP-GOF mutations in pancreatic ß-cells developed severe diabetes but did not show learning and memory deficits, suggesting neuronal KATP-GOF as promoting these features. These findings suggest a possible origin of cognitive dysfunction in DEND and the need for novel drugs to treat neurological features induced by neuronal KATP-GOF.

Compound heterozygous variants of the NARS2 gene in siblings with developmental delay, epilepsy, and neonatal diabetes syndrome.

Neonatal diabetes mellitus (NDM) with developmental delay and epilepsy is classified as developmental delay, epilepsy, and neonatal diabetes (DEND) syndrome. The majority of DEND syndrome are due to severely damaging variants of K-ATP channels, and few mitochondria-related genes have been reported. We report here two Japanese siblings who were clinically diagnosed with DEND syndrome in whom NARS2 compound heterozygous variants were detected. Patient 1 was a 3-year-old girl and presented with diabetes ketoacidosis at 3 months old. Patient 2 was a 1-year-old boy who presented with severe hyperglycemia and started insulin therapy at 3 days old. After the first episodes, they both presented with severe developmental delay, hearing loss and treatment-resistant epilepsy accompanied by progressive brain atrophy. Whole-exome sequencing revealed compound heterozygous NARS2 p.R159C and p.L217V variants, and the GATA4 p.P407Q variant in both patients. They were treated by mitochondrial supportive therapy of vitamin B1, L-carnitine, and coenzyme Q10. Patient 2 was withdrawn from insulin therapy at 6 months old. This is the first report of NDM in which variants of the NARS2 gene coding mitochondrial protein were detected. Genetic analysis including mitochondrial genes should be considered in patients with neonatal onset diabetes associated with neurogenic symptoms.

Precision Medicine: Long-Term Treatment with Sulfonylureas in Patients with Neonatal Diabetes Due to KCNJ11 Mutations.

PURPOSE OF REVIEW: The goal of this review is to provide updates on the safety and efficacy of long-term sulfonylurea use in patients with KCNJ11-related diabetes. Publications from 2004 to the present were reviewed with an emphasis on literature since 2014. RECENT FINDINGS: Sulfonylureas, often taken at high doses, have now been utilized effectively in KCNJ11 patients for over 10 years. Mild-moderate hypoglycemia can occur, but in two studies with a combined 975 patient-years on sulfonylureas, no severe hypoglycemic events were reported. Improvements in neurodevelopment and motor function after transition to sulfonylureas continue to be described. Sulfonylureas continue to be an effective, sustainable, and safe treatment for KCNJ11-related diabetes. Ongoing follow-up of patients in research registries will allow for deeper understanding of the facilitators and barriers to long-term sustainability. Further understanding of the effect of sulfonylurea on long-term neurodevelopmental outcomes, and the potential for adjunctive therapies, is needed.

DEND Syndrome with Heterozygous KCNJ11 Mutation Successfully Treated with Sulfonylurea.

Permanent neonatal diabetes mellitus (PNDM) is caused by mutations in the ATP-sensitive potassium channel (KATP channel) subunits. Developmental delay, epilepsy, and neonatal diabetes (DEND) syndrome is the most severe form of PNDM and is characterized by various neurologic features. We report on a patient with DEND syndrome following initial misdiagnosis with type 1 DM, who was successfully switched from insulin to sulfonylurea therapy. A 50-day-old male presented with fever and seizure, complicated by persistent hyperglycemia. Insulin therapy was initiated. At 10 months of age, the patient was unable to hold his head up and make eye contact with others. At 17.9 years of age, direct sequencing of KCNJ11 identified a heterozygous mutation of c.602G>A (p.R201H). Since then, treatment with gliclazide was initiated and the insulin dose was gradually reduced. Following 3 months, insulin was discontinued with a gliclazide dose of 2.4 mg/kg. The patient continued to have excellent glycemic control with a glycated hemoglobin (HbA1c) level of 5.8% after 5 months. However, the patient's psychomotor retardation did not improve. This study reports the first case of DEND syndrome in Korea caused by a KCNJ11 mutation and emphasizes the necessity to screen mutations in KATP channel genes in patients with neonatal diabetes.

Glycemic control and motor development in a patient with intermediate DEND.

The most common cause of neonatal diabetes, KCNJ11 gene mutation, can manifest as a neurological disorder. The most severe form consists of a constellation of developmental delay, epilepsy, and neonatal diabetes (DEND). Intermediate DEND (iDEND) refers to a milder presentation without epilepsy. We present a child with iDEND, for whom insulin injections were replaced with glibenclamide therapy at 17 months of age because of poor glycemic control and delayed motor development. Three months after initiation of glibenclamide, HbA1c decreased from 10.2% to 5.6%. Continuous glucose monitoring indicated that blood glucose fluctuations were suppressed while on glibenclamide. Furthermore, after initiating glibenclamide therapy, the developmental quotient (DQ) for motor ability markedly improved from 60 to 91, whereas the DQ for language and adoptive ability remained as they had been before the sulfonylurea treatment. Sulfonylurea treatment improved glycemic control and motor development in the present patient.

Development of IKATP Ion Channel Blockers Targeting Sulfonylurea Resistant Mutant KIR6.2 Based Channels for Treating DEND Syndrome.

Introduction: DEND syndrome is a rare channelopathy characterized by a combination of developmental delay, epilepsy and severe neonatal diabetes. Gain of function mutations in the KCNJ11 gene, encoding the KIR6.2 subunit of the IKATP potassium channel, stand at the basis of most forms of DEND syndrome. In a previous search for existing drugs with the potential of targeting Cantú Syndrome, also resulting from increased IKATP, we found a set of candidate drugs that may also possess the potential to target DEND syndrome. In the current work, we combined Molecular Modelling including Molecular Dynamics simulations, with single cell patch clamp electrophysiology, in order to test the effect of selected drug candidates on the KIR6.2 WT and DEND mutant channels. Methods: Molecular dynamics simulations were performed to investigate potential drug binding sites. To conduct in vitro studies, KIR6.2 Q52R and L164P mutants were constructed. Inside/out patch clamp electrophysiology on transiently transfected HEK293T cells was performed for establishing drug-channel inhibition relationships. Results: Molecular Dynamics simulations provided insight in potential channel interaction and shed light on possible mechanisms of action of the tested drug candidates. Effective IKIR6.2/SUR2a inhibition was obtained with the pore-blocker betaxolol (IC50 values 27-37 µM). Levobetaxolol effectively inhibited WT and L164P (IC50 values 22 µM) and Q52R (IC50 55 µM) channels. Of the SUR binding prostaglandin series, travoprost was found to be the best blocker of WT and L164P channels (IC50 2-3 µM), while Q52R inhibition was 15-20% at 10 µM. Conclusion: Our combination of MD and inside-out electrophysiology provides the rationale for drug mediated IKATP inhibition, and will be the basis for 1) screening of additional existing drugs for repurposing to address DEND syndrome, and 2) rationalized medicinal chemistry to improve IKATP inhibitor efficacy and specificity.

Severe Developmental Delay, Epilepsy and Neonatal Diabetes (DEND) Syndrome: A Case Report.

Developmental delay, Epilepsy and Neonatal Diabetes (DEND) syndrome is the most severe form of Permanent Neonatal Diabetes with KCNJ11 gene mutation which accounts for most of the cases. We report the first DEND syndrome in Malaysia with heterozygous missense mutation Q52R at KCNJ11 (Kir6.2) gene with delayed presentation beyond 6 months of age and failure to transition to glibenclamide. This report signifies the phenotypical variability among patients with the same genetic mutation and the different response to treatment.

Clinical features and partial proportional molecular genetics in neonatal diabetes mellitus: a retrospective analysis in southwestern China.

PURPOSE: To explore the relationship of phenotype and genotype of neonatal diabetes mellitus (NDM) in southwestern China. METHODS: Sixteen cases of NDM admitted to Children's Hospital of Chongqing Medical University from May 2009 to May 2019 were included in this study. The clinical features of the included infants were retrospectively analyzed. Peripheral blood samples of the patients and their parents were collected for mutation detection. RESULTS: Among the 16 cases of NDM, 8 cases were permanent neonatal diabetes mellitus (PNDM) (including 3 clinical syndromes), and 3 cases were transient neonatal diabetes mellitus (TNDM). Mutation detection was performed in six cases. The mutation genes and their loci were FOXP3 p.V408M, KCNJ11 p.C166Y, ABCC8 p.S830P, KCNJ11 p.I182T, KCNJ11 p.G334D, and ZFP57 p.R125X,412. ABCC8 p.S830P was the new found pathogenic site of gene mutation. According to the clinical features and follow-up results, one case was diagnosed as IPEX syndrome, two as DEND syndrome, two as simple PNDM, and one as TNDM. All the TNDM could spontaneously alleviate and then insulin was withdrawn. In PNDM, 75% of those with KATP channel gene mutation could be completely or partially converted to oral sulfonylureas treatment, however, the rest cases needed lifelong insulin replacement therapy. CONCLUSION: The clinical manifestations and treatment regimens of patients with NDM vary according to the type of gene mutation. Even the same mutant genotype has differences in phenotype and response to treatment.

Methods for Characterizing Disease-Associated ATP-Sensitive Potassium Channel Mutations.

The ATP-sensitive potassium (KATP) channel formed by the inwardly rectifying potassium channel Kir6.2 and the sulfonylurea receptor 1 (SUR1) plays a key role in regulating insulin secretion. Genetic mutations in KCNJ11 or ABCC8 which encode Kir6.2 and SUR1 respectively are major causes of insulin secretion disorders: those causing loss of channel function lead to congenital hyperinsulinism, whereas those causing gain of channel function result in neonatal diabetes and in some cases developmental delay, epilepsy, and neonatal diabetes, referred to as the DEND syndrome. Understanding how disease mutations disrupt channel expression and function is important for disease diagnosis and for devising effective therapeutic strategies. Here, we describe a workflow including several biochemical and functional assays to assess the effects of mutations on channel expression and function.

KATP Channel Mutations and Neonatal Diabetes.

Since the discovery of the KATP channel in 1983, numerous studies have revealed its physiological functions. The KATP channel is expressed in various organs, including the pancreas, brain and skeletal muscles. It functions as a "metabolic sensor" that converts the metabolic status to electrical activity. In pancreatic beta-cells, the KATP channel regulates the secretion of insulin by sensing a change in the blood glucose level and thus maintains glucose homeostasis. In 2004, heterozygous gain-of-function mutations in the KCNJ11 gene, which encodes the Kir6.2 subunit of the KATP channel, were found to cause neonatal diabetes. In some mutations, diabetes is accompanied by severe neurological symptoms [developmental delay, epilepsy, neonatal diabetes (DEND) syndrome]. This review focuses on mutations of Kir6.2, the pore-forming subunit and sulfonylurea receptor (SUR) 1, the regulatory subunit of the KATP channel, which cause neonatal diabetes/DEND syndrome and also discusses the findings of the pathological mechanisms that are associated with neonatal diabetes, and its neurological features.

Successful transition to sulfonylurea in neonatal diabetes, developmental delay, and seizures (DEND syndrome) due to R50P KCNJ11 mutation.

Mutations in KCNJ11 cause majority of cases of permanent neonatal diabetes (PND). Multiple reports of PND with successful transitioning to oral sulfonylurea had been reported except for those with DEND syndrome. This case report highlights a case of successful sulfonylurea treatment in a patient with DEND syndrome.

Organization of cGMP sensing structures on the rod photoreceptor outer segment plasma membrane.

A diffusion barrier segregates the plasma membrane of the rod photoreceptor outer segment into 2 domains; one which is optimized for the conductance of ions in the phototransduction cascade and another for disk membrane synthesis. We propose the former to be named "phototransductive plasma membrane domain," and the latter to be named "disk morphogenic plasma membrane domain." Within the phototransductive plasma membrane, cGMP-gated channels are concentrated in striated membrane features, which are proximally located to the sites of active cGMP production within the disk membranes. For proper localization of cGMP-gated channel to the phototransductive plasma membrane, the glutamic acid-rich protein domain encoded in the ß subunit plays a critical role. Quantitative study suggests that the disk morphogenic domain likely plays an important role in enriching rhodopsin prior to its sequestration into closed disk membranes. Thus, this and our previous studies provide new insight into the mechanism that spatially organizes the vertebrate phototransduction cascade.