Intellectual Disability in KATP Channel Neonatal Diabetes

Monogenic diabetes: An evidence-based clinical approach

Monogenic diabetes is a heterogeneous disorder characterized by hyperglycemia arising from defects in a single gene. Maturity-onset diabetes of the young (MODY) is the most common type with 14 subtypes, each linked to specific mutations affecting insulin synthesis, secretion and glucose regulation. Common traits across MODY subtypes include early-onset diabetes, a family history of autosomal dominant diabetes, lack of features of insulin resistance, and absent islet cell autoimmunity. Many cases are misdiagnosed as type 1 and type 2 diabetes mellitus. Biomarkers and scoring systems can help identify candidates for genetic testing. GCK-MODY, a common subtype, manifests as mild hyperglycemia and doesn’t require treatment except during pregnancy. In contrast, mutations in HNF4A, HNF1A, and HNF1B genes lead to progressive beta-cell failure and similar risks of complications as type 2 diabetes mellitus. Neonatal diabetes mellitus (NDM) is a rare form of monogenic diabetes that usually presents within the first six months. Half of the cases are lifelong, while others experience transient remission. Permanent NDM is most commonly due to activating mutations in genes encoding the adenosine triphosphate-sensitive potassium channel (KCNJ11 or ABCC8) and can be transitioned to sulfonylurea after confirmation of diagnosis. Thus, in many cases, monogenic diabetes offers an opportunity to provide precision treatment. The scope has broadened with next-generation sequencing (NGS) technologies, replacing older methods like Sanger sequencing. NGS can be for targeted gene panels, whole-exome sequencing (WES), or whole-genome sequencing. Targeted gene panels offer specific information efficiently, while WES provides comprehensive data but comes with bioinformatic challenges. The surge in testing has also led to an increase in variants of unknown significance (VUS). Deciding whether VUS is disease-causing or benign can be challenging. Computational models, functional studies, and clinical knowledge help to determine pathogenicity. Advances in genetic testing technologies offer hope for improved diagnosis and personalized treatment but also raise concerns about interpretation and ethics.

Novel mutations found in genes involved in global developmental delay and intellectual disability by whole-exome sequencing, homology modeling, and systems biology

BACKGROUND

Genes associated with global developmental delay (GDD) and intellectual disability (ID) are increasingly being identified through next-generation sequencing (NGS) technologies. This study aimed to identify novel mutations in GDD/ID phenotypes through whole-exome sequencing (WES) and additional in silico analyses.

MATERIAL AND METHODS

WES was performed on 27 subjects, among whom 18 were screened for potential novel mutations. In silico analyses included protein-protein interactions (PPIs), gene-miRNA interactions (GMIs), and enrichment analyses. The identified novel variants were further modelled using I-Tasser-MTD and SWISS-MODEL, with structural superimposition performed.

RESULTS

Novel mutations were detected in 18 patients, with 10 variants reported for the first time. Among these, three were classified as pathogenic (DNMT1:c.856dup, KCNQ2:c.1635_1636insT, and TMEM94:c.2598_2599insC), and six were likely pathogenic. DNMT1 and MRE11 were highlighted as key players in PPIs and GMIs. GMIs analysis emphasised the roles of hsa-miR-30a-5p and hsa-miR-185-5p. The top-scoring pathways included the neuronal system (R-HSA-112316, p = 7.73E-04) and negative regulation of the smooth muscle cell apoptotic process (p = 3.37E-06). Homology modelling and superimposition revealed a significant functional loss in the mutated DNMT1 enzyme structure.

CONCLUSION

This study identified 10 novel pathogenic/likely pathogenic variants associated with GDD/ID, supported by clinical findings and in silico analyses focused on DNMT1 mutations.

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 hypothesized 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.

Neonatal diabetes mellitus around the world: Update 2024

Neonatal diabetes mellitus (NDM), defined as diabetes with an onset during the first 6 months of life, is a rare form of monogenic diabetes. The initial publications on this condition began appearing in the second half of the 1990s and quite surprisingly, the search for new NDM genes is still ongoing with great vigor. Between 2018 and early 2024, six brand new NDM-genes have been discovered (CNOT1, FICD, ONECUT1, PDIA6, YIPF5, ZNF808) and three genes known to cause different diseases were identified as NDM-genes (EIF2B1, NARS2, KCNMA1). In addition, NDM cases carrying mutations in three other genes known to give rise to diabetes during childhood have been also identified (AGPAT2, BSCL2, PIK3R1). As a consequence, the list of NDM genes now exceeds 40. This genetic heterogeneity translates into many different mechanism(s) of disease that are being investigated with state-of-the-art methodologies, such as induced pluripotent stem cells (iPSC) and human embryonic stem cells (hESC) manipulated with the CRISPR technique of genome editing. This diversity in genetic causes and the pathophysiology of diabetes dictate the need for a variety of therapeutic approaches. The aim of this paper is to provide an overview on recent achievements in all aspects of this area of research.

Potassium channels in behavioral brain disorders. Molecular mechanisms and therapeutic potential: A narrative review

Potassium channels (K+-channels) selectively control the passive flow of potassium ions across biological membranes and thereby also regulate membrane excitability. Genetic variants affecting many of the human K+-channels are well known causes of Mendelian disorders within cardiology, neurology, and endocrinology. K+-channels are also primary targets of many natural toxins from poisonous organisms and drugs used within cardiology and metabolism. As genetic tools are improving and larger clinical samples are being investigated, the spectrum of clinical phenotypes implicated in K+-channels dysfunction is rapidly expanding, notably within immunology, neurosciences, and metabolism. K+-channels that previously were considered to be expressed in only a few organs and to have discrete physiological functions, have recently been found in multiple tissues and with new, unexpected functions. The pleiotropic functions and patterns of expression of K+-channels may provide additional therapeutic opportunities, along with new emerging challenges from off-target effects. Here we review the functions and therapeutic potential of K+-channels, with an emphasis on the nervous system, roles in neuropsychiatric disorders and their involvement in other organ systems and diseases.

Case report: Neonatal diabetes mellitus caused by KCNJ11 mutation presenting with intracranial hemorrhage

Neonatal diabetes mellitus (NDM) is a rare type of monogenic diabetes. At present, most published studies have focused on the types of gene mutations associated with NDM and the therapeutic effect of sulfonylureas (SUs) on the disease; few studies on NDM-associated intracranial hemorrhage (ICH) exist. In addition, p.V59M mutations generally lead to intermediate DEND (iDEND: intermediate developmental delay and neonatal diabetes) syndrome without epilepsy. Here, we present a case of a 1-month-old male infant who was diagnosed with NDM caused by a KCNJ11 missense mutation (p.V59M), presenting with cerebral injury. In the early stage of the disease, continuous insulin dose adjustment did not achieve an ideal level of blood glucose. Although blood glucose was subsequently controlled by oral SUs, which were administered after the genetic test result, the patient still displayed epilepsy and developmental delay. In this case report, we present our experience in the treatment of the infant, switching from insulin to oral SUs and we thought that SUs have limited effects on improving the prognosis of neurodevelopmental disturbances in NDM with foci of encephalomalacia. In addition, there may be a relationship between KCNJ11 missense mutations and cerebral injury, and further research must be carried out to confirm these points.

Sulfonylurea for improving neurological features in neonatal diabetes: A systematic review and meta-analyses

OBJECTIVE

In monogenic diabetes due to KCNJ11 and ABCC8 mutations that impair KATP- channel function, sulfonylureas improve long-term glycemic control. Although KATP channels are extensively expressed in the brain, the effect of sulfonylureas on neurological function has varied widely. We evaluated published evidence about potential effects of sulfonylureas on neurological features, especially epilepsy, cognition, motor function and muscular tone, visuo-motor integration, and attention deficits in children and adults with KCNJ11 and ABCC8-related neonatal-onset diabetes mellitus.

RESEARCH DESIGN AND METHODS

We conducted a systematic review and meta-analyses of the literature (PROSPERO, CRD42021254782), including individual-patient data, according to PRISMA, using RevMan software. We also graded the level of evidence.

RESULTS

We selected 34 of 776 publications. The evaluation of global neurological function before and after sulfonylurea (glibenclamide) treatment in 114 patients yielded a risk difference (RD) of 58% (95%CI, 43%-74%; I²  = 54%) overall and 73% (95%CI, 32%-113%; I²  = 0%) in the subgroup younger than 4 years; the level of evidence was moderate and high, respectively. EEG studies of epilepsy showed a RD of 56% (95%CI, 23%-89%; I²  = 34%) in patients with KCNJ11 mutations, with a high quality of evidence. For hypotonia and motor function, the RDs were 90% (95%CI, 69%-111%; I²  = 0%) and 73% (95%CI, 35%-111%; I²  = 0%), respectively, with a high level of evidence.

CONCLUSIONS

Glibenclamide significantly improved neurological abnormalities in patients with neonatal-onset diabetes due to KCNJ11 or ABCC8 mutations. Hypotonia was the symptom that responded best. Earlier treatment initiation was associated with greater benefits.

Functional Regulation of KATP Channels and Mutant Insight Into Clinical Therapeutic Strategies in Cardiovascular Diseases

ATP-sensitive potassium channels (KATP channels) play pivotal roles in excitable cells and link cellular metabolism with membrane excitability. The action potential converts electricity into dynamics by ion channel-mediated ion exchange to generate systole, involved in every heartbeat. Activation of the KATP channel repolarizes the membrane potential and decreases early afterdepolarization (EAD)-mediated arrhythmias. KATP channels in cardiomyocytes have less function under physiological conditions but they open during severe and prolonged anoxia due to a reduced ATP/ADP ratio, lessening cellular excitability and thus preventing action potential generation and cell contraction. Small active molecules activate and enhance the opening of the KATP channel, which induces the repolarization of the membrane and decreases the occurrence of malignant arrhythmia. Accumulated evidence indicates that mutation of KATP channels deteriorates the regulatory roles in mutation-related diseases. However, patients with mutations in KATP channels still have no efficient treatment. Hence, in this study, we describe the role of KATP channels and subunits in angiocardiopathy, summarize the mutations of the KATP channels and the functional regulation of small active molecules in KATP channels, elucidate the potential mechanisms of mutant KATP channels and provide insight into clinical therapeutic strategies.

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

ATP-sensitive potassium (K_ATP) gain-of-function (GOF) mutations cause neonatal diabetes, with some individuals exhibiting developmental delay, epilepsy, and neonatal diabetes (DEND) syndrome. Mice expressing K_ATP-GOF mutations pan-neuronally (nK_ATP-GOF) demonstrated sensorimotor and cognitive deficits, whereas hippocampus-specific hK_ATP-GOF mice exhibited mostly learning and memory deficiencies. Both nK_ATP-GOF and hK_ATP-GOF mice showed altered neuronal excitability and reduced hippocampal long-term potentiation (LTP). Sulfonylurea therapy, which inhibits K_ATP, mildly improved sensorimotor but not cognitive deficits in K_ATP-GOF mice. Mice expressing K_ATP-GOF mutations in pancreatic β-cells developed severe diabetes but did not show learning and memory deficits, suggesting neuronal K_ATP-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 K_ATP-GOF.

Long-term Follow-up of Glycemic and Neurological Outcomes in an International Series of Patients With Sulfonylurea-Treated ABCC8 Permanent Neonatal Diabetes

OBJECTIVE

ABCC8 mutations cause neonatal diabetes mellitus that can be transient (TNDM) or, less commonly, permanent (PNDM); ∼90% of individuals can be treated with oral sulfonylureas instead of insulin. Previous studies suggested that people with ABCC8-PNDM require lower sulfonylurea doses and have milder neurological features than those with KCNJ11-PNDM. However, these studies were short-term and included combinations of ABCC8-PNDM and ABCC8-TNDM. We aimed to assess the long-term glycemic and neurological outcomes in sulfonylurea-treated ABCC8-PNDM.

RESEARCH DESIGN AND METHODS

We studied all 24 individuals with ABCC8-PNDM diagnosed in the U.K., Italy, France, and U.S. known to transfer from insulin to sulfonylureas before May 2010. Data on glycemic control, sulfonylurea dose, adverse effects including hypoglycemia, and neurological features were analyzed using nonparametric statistical methods.

RESULTS

Long-term data were obtained for 21 of 24 individuals (median follow-up 10.0 [range 4.1-13.2] years). Eighteen of 21 remained on sulfonylureas without insulin at the most recent follow-up. Glycemic control improved on sulfonylureas (presulfonylurea vs. 1-year posttransfer HbA1c 7.2% vs. 5.7%, P = 0.0004) and remained excellent long-term (1-year vs. 10-year HbA1c 5.7% vs. 6.5%, P = 0.04), n = 16. Relatively high doses were used (1-year vs. 10-year dose 0.37 vs. 0.25 mg/kg/day glyburide, P = 0.50) without any severe hypoglycemia. Neurological features were reported in 13 of 21 individuals; these improved following sulfonylurea transfer in 7 of 13. The most common features were learning difficulties (52%), developmental delay (48%), and attention deficit hyperactivity disorder (38%).

CONCLUSIONS

Sulfonylurea treatment of ABCC8-PNDM results in excellent long-term glycemic control. Overt neurological features frequently occur and may improve with sulfonylureas, supporting early, rapid genetic testing to guide appropriate treatment and neurodevelopmental assessment.

The clinical consequences of heterogeneity within and between different diabetes types

Advances in molecular methods and the ability to share large population-based datasets are uncovering heterogeneity within diabetes types, and some commonalities between types. Within type 1 diabetes, endotypes have been discovered based on demographic (e.g. age at diagnosis, race/ethnicity), genetic, immunological, histopathological, metabolic and/or clinical course characteristics, with implications for disease prediction, prevention, diagnosis and treatment. In type 2 diabetes, the relative contributions of insulin resistance and beta cell dysfunction are heterogeneous and relate to demographics, genetics and clinical characteristics, with substantial interaction from environmental exposures. Investigators have proposed approaches that vary from simple to complex in combining these data to identify type 2 diabetes clusters relevant to prognosis and treatment. Advances in pharmacogenetics and pharmacodynamics are also improving treatment. Monogenic diabetes is a prime example of how understanding heterogeneity within diabetes types can lead to precision medicine, since phenotype and treatment are affected by which gene is mutated. Heterogeneity also blurs the classic distinctions between diabetes types, and has led to the definition of additional categories, such as latent autoimmune diabetes in adults, type 1.5 diabetes and ketosis-prone diabetes. Furthermore, monogenic diabetes shares many features with type 1 and type 2 diabetes, which make diagnosis difficult. These challenges to the current classification framework in adult and paediatric diabetes require new approaches. The 'palette model' and the 'threshold hypothesis' can be combined to help explain the heterogeneity within and between diabetes types. Leveraging such approaches for therapeutic benefit will be an important next step for precision medicine in diabetes. Graphical abstract.

Intellectual Disability and Potassium Channelopathies: A Systematic Review

Intellectual disability (ID) manifests prior to adulthood as severe limitations to intellectual function and adaptive behavior. The role of potassium channelopathies in ID is poorly understood. Therefore, we aimed to evaluate the relationship between ID and potassium channelopathies. We hypothesized that potassium channelopathies are strongly associated with ID initiation, and that both gain- and loss-of-function mutations lead to ID. This systematic review explores the burden of potassium channelopathies, possible mechanisms, advancements using animal models, therapies, and existing gaps. The literature search encompassed both PubMed and Embase up to October 2019. A total of 75 articles describing 338 cases were included in this review. Nineteen channelopathies were identified, affecting the following genes: KCNMA1, KCNN3, KCNT1, KCNT2, KCNJ10, KCNJ6, KCNJ11, KCNA2, KCNA4, KCND3, KCNH1, KCNQ2, KCNAB1, KCNQ3, KCNQ5, KCNC1, KCNB1, KCNC3, and KCTD3. Twelve of these genes presented both gain- and loss-of-function properties, three displayed gain-of-function only, three exhibited loss-of-function only, and one had unknown function. How gain- and loss-of-function mutations can both lead to ID remains largely unknown. We identified only a few animal studies that focused on the mechanisms of ID in relation to potassium channelopathies and some of the few available therapeutic options (channel openers or blockers) appear to offer limited efficacy. In conclusion, potassium channelopathies contribute to the initiation of ID in several instances and this review provides a comprehensive overview of which molecular players are involved in some of the most prominent disease phenotypes.