Successful sulfonylurea treatment of a neonate with neonatal diabetes mellitus due to a new KCNJ11 mutation

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.

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.

Recent Advances in Neonatal Diabetes

Neonatal diabetes mellitus (DM) is defined by the onset of persistent hyperglycemia within the first six months of life but may present up to 12 months of life. A gene mutation affecting pancreatic beta cells or synthesis/secretion of insulin is present in more than 80% of the children with neonatal diabetes. Neonatal DM can be transient, permanent, or be a component of a syndrome. Genetic testing is important as a specific genetic mutation can significantly alter the treatment and outcome. Patients with mutations of either KCNJ11 or ABCC8 that encode subunits of the K_ATP channel gene mutation can be managed with sulfonylurea oral therapy while patients with other genetic mutations require insulin treatment.

Successful sulfonylurea treatment of a neonate with neonatal diabetes mellitus due to a novel missense mutation, p.P1199L, in the ABCC8 gene

Neonatal/infancy-onset diabetes mellitus is a monogenic form of diabetes with onset within 6 months of age. Two distinct types of neonatal diabetes mellitus have been recognized: permanent and transient. Mutations within the K(+)ATP channel and insulin genes are found in most patients with permanent diabetes mellitus. There have been several reports of the successful transition from insulin to sulfonylurea agents in patients with permanent diabetes mellitus caused by mutations in the KCNJ11 gene. We report on a term female neonate with a novel missense mutation, p.P1199L, in the ABCC8 gene that encodes the sulfonylurea receptor 1 whose treatment was successfully converted from insulin to sulfonylurea.