Genotype-phenotype correlation of KATP channel gene defects causing permanent neonatal diabetes in Indian patients

Genetic variant profiling of neonatal diabetes mellitus in Iranian patients: Unveiling 58 distinct variants in 14 genes

INTRODUCTION

Neonatal diabetes mellitus (NDM) is a rare non-immunological monogenic disorder characterized by hyperglycemic conditions primarily occurring within the first 6 months of life. The majority of cases are attributed to pathogenic variants in genes affecting beta-cell survival, insulin regulation, and secretion. This study aims to investigate the genetic landscape of NDM in Iran.

METHODS

We recruited a total of 135 patients who were initially diagnosed with diabetes at <12 months of age in Iran and referred to pediatric endocrinology clinics across the country. These patients underwent genetic diagnostic tests conducted by the Exeter Molecular Genetics Laboratory in the UK. The pathogenic variants identified were sorted and described based on type, pathogenicity (according to ACMG/AMP criteria), novelty, and the affected protein domain.

RESULTS

Genetic defects were identified in 93 probands, presenting various pathogenic abnormalities associated with NDM and its associated syndromes. 76% of the patients were born as a result of consanguineous marriage, and a familial history of diabetes was found in 43% of the cases. A total of 58 distinct variants in 14 different genes were discovered, including 20 variants reported for the first time. Causative variants were most frequently identified in EIF2AK3, KCNJ11, and ABCC8, respectively. Notably, EIF2AK3 and ABCC8 exhibited the highest number of novel variants.

DISCUSSION

These findings provide valuable insights into the genetic landscape of NDM in the Iranian population and contribute to the knowledge of novel pathogenic variants within known causative genes.

A novel stop-loss mutation in NKX2-2 gene as a cause of neonatal diabetes mellitus: molecular characterization and structural analysis

AIM

To identify the genetic etiology of neonatal diabetes in an infant and to elucidate the molecular mechanism of the identified mutation underlying the pathogenesis.

METHODS

Genetic analysis was carried out by sequencing of known etiological genes associated with NDM. Molecular characterization was performed by constructing a identified mutation in NKX2-2 gene and  functional aspects was tested using transactivation, protein expression, DNA binding, nuclear localization assays. Structural analysis was performed by modeling the NKX2-2 protein structure.

RESULTS

A novel homozygous frameshift mutation  c.772delC, p.Q258SFs*59 in the NKX2-2 gene was identified in a patient with neonatal diabetes. Functional studies revealed that this mutation resulted in an elongated protein sequence, affecting DNA binding activity and transcriptional function. Structural analysis suggested alterations in the protein's tertiary structure, likely contributing to its dysfunction.

CONCLUSION

This study presents the first report of a stop-loss mutation in the NKX2-2 gene associated with NDM. Our findings emphasize the importance of functional and structural characterization to understand the biological consequences of such mutations. This comprehensive analysis provides insights into the molecular mechanisms underlying NDM and its clinical phenotype, which may aid in better diagnosis and management of patients with similar variants in the future.

Genetics and Natural History of Non-pancreatectomized Patients With Congenital Hyperinsulinism Due to Variants in ABCC8

CONTEXT

Patients with congenital hyperinsulinism due to ABCC8 variants generally present severe hypoglycemia and those who do not respond to medical treatment typically undergo pancreatectomy. Few data exist on the natural history of non-pancreatectomized patients.

OBJECTIVE

This work aims to describe the genetic characteristics and natural history in a cohort of non-pancreatectomized patients with congenital hyperinsulinism due to variants in the ABCC8 gene.

METHODS

Ambispective study of patients with congenital hyperinsulinism with pathogenic or likely pathogenic variants in ABCC8 treated in the last 48 years and who were not pancreatectomized. Continuous glucose monitoring (CGM) has been periodically performed in all patients since 2003. An oral glucose tolerance test was performed if hyperglycemia was detected in the CGM.

RESULTS

Eighteen non-pancreatectomized patients with ABCC8 variants were included. Seven (38.9%) patients were heterozygous, 8 (44.4%) compound heterozygous, 2 (11.1%) homozygous, and 1 patient carried 2 variants with incomplete familial segregation studies. Seventeen patients were followed up and 12 (70.6%) of them evolved to spontaneous resolution (median age 6.0 ± 4 years; range, 1-14). Five of these 12 patients (41.7%) subsequently progressed to diabetes with insufficient insulin secretion. Evolution to diabetes was more frequent in patients with biallelic variants in the ABCC8 gene.

CONCLUSION

The high remission rate observed in our cohort makes conservative medical treatment a reliable strategy for the management of patients with congenital hyperinsulinism due to ABCC8 variants. In addition, a periodic follow-up of glucose metabolism after remission is recommended, as a significant proportion of patients evolved to impaired glucose tolerance or diabetes (biphasic phenotype).

Maturity-Onset Diabetes of the Young: Mutations, Physiological Consequences, and Treatment Options

Maturity-Onset Diabetes of the Young (MODY) is a rare form of diabetes which affects between 1% and 5% of diagnosed diabetes cases. Clinical characterizations of MODY include onset of diabetes at an early age (before the age of 30), autosomal dominant inheritance pattern, impaired glucose-induced secretion of insulin, and hyperglycemia. Presently, 14 MODY subtypes have been identified. Within these subtypes are several mutations which contribute to the different MODY phenotypes. Despite the identification of these 14 subtypes, MODY is often misdiagnosed as type 1 or type 2 diabetes mellitus due to an overlap in clinical features, high cost and limited availability of genetic testing, and unfamiliarity with MODY outside of the medical profession. The primary aim of this review is to investigate the genetic characterization of the MODY subtypes. Additionally, this review will elucidate the link between the genetics, function, and clinical manifestations of MODY in each of the 14 subtypes. In providing this knowledge, we hope to assist in the accurate diagnosis of MODY patients and, subsequently, in ensuring they receive appropriate treatment.

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

ATP-sensitive potassium channels (K_ATP 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 K_ATP channel repolarizes the membrane potential and decreases early afterdepolarization (EAD)-mediated arrhythmias. K_ATP 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 K_ATP channel, which induces the repolarization of the membrane and decreases the occurrence of malignant arrhythmia. Accumulated evidence indicates that mutation of K_ATP channels deteriorates the regulatory roles in mutation-related diseases. However, patients with mutations in K_ATP channels still have no efficient treatment. Hence, in this study, we describe the role of K_ATP channels and subunits in angiocardiopathy, summarize the mutations of the K_ATP channels and the functional regulation of small active molecules in K_ATP channels, elucidate the potential mechanisms of mutant K_ATP channels and provide insight into clinical therapeutic strategies.

Insulin gene mutations linked to permanent neonatal diabetes mellitus in Indian population

BACKGROUND AND AIM

Neonatal diabetes mellitus (NDM) is a rare monogenic disorder of pancreatic beta cell mass and/or function. In the present study we aimed to evaluate the INS gene mutations in a cohort of children with Permanent Neonatal Diabetes Mellitus (PNDM) and to explore the clinical and genetic characteristics of PNDM caused by INS mutations.

METHODS

Direct sequencing of all exons of INS genes was carried out in 189 children with PNDM. Clinical and biochemical data were collected and correlated. The pathogenicity of mutations was determined based on the American College of Medical Genetics and Genomics and Association of Medical Pathology guidelines.

RESULTS

Two novel mutations (His34Pro, Leu35Met) in a compound heterozygous state and seven known mutations (Gly32Ser, Phe48Cys, Arg89Cys, Cys96Tyr, Ser98Ile, Try108Asp and Cys109Phe) in the INS gene were identified in 8 patients out of the total of 189 PNDM children studied. Four mutations were involved in defects with disulphide bond formation and hence were in crucial regions of the gene. All the mutations were de novo in origin.

CONCLUSIONS

This is the first comprehensive study from India to investigate the insulin gene mutations in PNDM and to show that INS gene mutations also contribute to the causation of PNDM.

Molecular Genetics, Clinical Characteristics, and Treatment Outcomes of KATP-Channel Neonatal Diabetes Mellitus in Vietnam National Children's Hospital

BACKGROUND

Neonatal diabetes mellitus (NDM) is defined as insulin-requiring persistent hyperglycemia occurring within the first 6 months of life, which can result from mutations in at least 25 different genes. Activating heterozygous mutations in genes encoding either of the subunits of the ATP-sensitive K⁺ channel (K_ATP channel; KCNJ11 or ABCC8) of the pancreatic beta cell are the most common cause of permanent NDM and the second most common cause of transient NDM. Patients with NDM caused by K_ATP channel mutations are sensitive to sulfonylurea (SU) treatment; therefore, their clinical management can be improved by replacing insulin with oral agents.

PATIENTS AND METHODS

Seventy patients were diagnosed with NDM between May 2008 and May 2021 at Vietnam National Children's Hospital, and molecular genetic testing for all genes known to cause NDM was performed at the Exeter Genomic Laboratory, UK. Patients with ABCC8 or KCNJ11 mutations were transferred from insulin to oral SU. Clinical characteristics, molecular genetics, and annual data relating to glycemic control, SU dose, severe hypoglycemia, and side effects were collected. The main outcomes of interest were SU dose, SU failure (defined as permanent reintroduction of daily insulin), and glycemic control (HbA1c).

RESULTS

Fifty-four of 70 patients (77%) with NDM harbored a genetic mutation and of these; 27 (50%) had activating heterozygous mutations in ABCC8 or KCNJ11. A total of 21 pathogenic mutations were identified in the 27 patients, including 13 mutations in ABCC8 and 8 mutations in KCNJ11. Overall, 51% had low birth weight (below 3rd percentile), 23 (85%) were diagnosed before 3 months of age, and 23 (85%) presented with diabetic ketoacidosis. At diagnosis, clinical and biochemical findings (mean ± SD) were pH 7.16 ± 0.16; HCO3- , 7.9 ± 7.4 mmol/L; BE, -17.9 ± 9.1 mmol/L; HbA1C, 7.98% ± 2.93%; blood glucose, 36.2 ± 12.3 mmol/L; and C-peptide median, 0.09 (range, 0-1.61 nmol/l). Twenty-six patients were successfully transferred from insulin to SU therapy. In the remaining case, remission of diabetes occurred prior to transfer. Glycemic control on SU treatment was better than on insulin treatment: HbA1c and blood glucose level decreased from 7.58% ± 4.63% and 19.04 ± 14.09 mmol/L when treated with insulin to 5.8 ± 0.94% and 6.87 ± 3.46 mmol/L when treated with SU, respectively.

CONCLUSIONS

This is the first case series of NDM patients with ABCC8/KCNJ11 mutations reported in Vietnam. SU is safe in the short term for these patients and more effective than insulin therapy, consistent with all studies to date. This is relevant for populations where access to and cost of insulin are problematic, reinforcing the importance of genetic testing for NDM.