Congenital hyperinsulinism is a rare disorder characterized by inappropriate insulin secretion, leading to persistent hypoglycemia. One genetic subtype, hyperinsulinism-hyperammonemia syndrome, results from activating mutations in the GLUD1 gene. This study aimed to describe the clinical spectrum, genetic variants, and outcomes of patients with GLUD1-related hyperinsulinism-hyperammonemia syndrome treated at a tertiary care center in Saudi Arabia. This retrospective case series included five patients of Saudi ethnicity diagnosed with GLUD1-associated hyperinsulinism-hyperammonemia syndrome between September and November 2023 at King Faisal Specialist Hospital and Research Centre. Clinical, biochemical, imaging, and genetic data were collected from medical records. Descriptive statistics were used to summarize the findings. All five patients (four pediatric, one adult) presented with hypoglycemia, elevated insulin levels, and persistent hyperammonemia. Genetic testing confirmed GLUD1 mutations in all cases, with two patients sharing the c.1493C > T (p.Ser498Leu) variant. Diazoxide therapy effectively controlled hypoglycemia in most patients. Two patients experienced significant neurological complications, including seizures and developmental delay. One adult patient underwent pancreatectomy with improvement in hypoglycemia control but retained chronic neurological sequelae. Brain magnetic resonance imaging abnormalities and secondary genetic variants were identified in two cases. GLUD1-related hyperinsulinism-hyperammonemia syndrome presents with a wide clinical spectrum, often with early onset and risk of neurological impairment if not promptly treated. Early diagnosis and individualized management-including genetic testing and diazoxide therapy-are essential to prevent irreversible complications. Further multicenter studies are warranted to better understand long-term outcomes in affected populations.

Backgroud: Glutamate dehydrogenase (GDH) is involved in the metabolism of glutamate and ammonia. It is regulated by multiple ligand variants, and hyper-active GDH mutants have been reported for hyperinsulinism hyperammonemia syndrome (HHS). Methods: Here, we constructed the wild-type human GDH and three human GDH454 mutants and investigated their degradation activity and performance under different GDH inhibitors. Results: Protein activity test and SDS-PAGE analysis of the purified proteins showed that the GDH454 mutant from HHS has weaker GDH enzymatic activity but greater resistance to trypsin hydrolysis than the wild type. Interestingly, using the biomolecular interactions technique, it showed that the GDH454 mutant has 109 times weaker affinity for trypsin and 10-fold weaker for epigallocatechin gallate (EGCG) than the wild-type GDH. Subsequently, native-PAGE gel analysis demonstrated that EGCG could break down the GDH hexamer into monomers and form a complex with trypsin to enhance the degradation of both types of GDH. Conclusions: EGCG showed good affinity to both the wild-type and the mutant GDH proteins, promoting protein degradation; this provides a new strategy for the treatment of HHS and other hyper-active GDH-related diseases.

Neonatal hypoglycemia (NH) is a common abnormality in newborns, posing significant morbidity risks. Prompt diagnosis and treatment are vital to mitigate brain damage and enhance outcomes. Congenital hyperinsulinemia (CHI) is a leading cause of recurrent hypoglycemia in infants, often stemming from genetic mutations such as in the GLUD1 gene, manifesting as hyperinsulinism-hyperammonemia syndrome (HI/HA). We present a case of a 2-year-old girl with refractory epilepsy, later identified as HI/HA, whose paroxysmal episodes mimicked multiple seizure types. Genetic testing revealed a heterozygous pathogenic mutation in exon 2 of the GLUD1 gene. Treatment with diazoxide significantly improved blood sugar levels and achieved effective seizure control. Our case underscores the significance of considering metabolic etiologies like hyperinsulinemic hypoglycemia in children with seizures resistant to standard antiepileptic drugs. Early recognition, genetic testing, and targeted therapy are pivotal for achieving seizure control and optimizing patient outcomes.

To highlight advances in congenital hyperinsulinism (HI), including newly described molecular mechanisms of disease, novel therapeutic interventions, and improved understanding of long-term outcomes. Important advances have been made elucidating the molecular mechanisms responsible for HI. Non-coding variants in HK1 have been found to cause aberrant hexokinase expression. Inactivating mutations in SLC25A36 have been identified in children with features of the hyperinsulinism hyperammonemia syndrome. Low-level mosaic mutations in known HI genes have been detected in cases of 'genetic testing negative' HI. Identification and localization of focal HI lesions remains a priority, since focal HI can be cured with surgery. Use of 68 Ga-NODAGA-exendin-4 PET has been proposed to localize focal lesions. Additional studies are needed before this technique replaces 18 F-DOPA PET as standard of care. Treatment options for children with diffuse HI remain limited. The long-acting somatostatin analog, lanreotide, was shown to significantly improve glycemic control in a large series of children with HI. New therapies are under development, with promising preliminary results. Long-term quality of life and neurodevelopmental outcomes remain suboptimal. Advanced genetic and epigenomic analytic techniques have uncovered novel molecular mechanisms of HI. Development of new drugs holds promise to improve long-term outcomes for individuals with HI.

Hyperinsulinism/hyperammonemia (HI/HA) syndrome has been known to be caused by dominant gain-of-function mutations in GLUD1, encoding the mitochondrial enzyme glutamate dehydrogenase. Pathogenic GLUD1 mutations enhance enzymatic activity by reducing its sensitivity to allosteric inhibition by GTP. Two recent independent studies showed that a similar HI/HA phenotype can be caused by biallelic mutations in SLC25A36, encoding pyrimidine nucleotide carrier 2 (PNC2), a mitochondrial nucleotide carrier that transports pyrimidine and guanine nucleotides across the inner mitochondrial membrane: one study reported a single case caused by a homozygous truncating mutation in SLC25A36 resulting in lack of expression of SLC25A36 in patients' fibroblasts. A second study described two siblings with a splice site mutation in SLC25A36, causing reduction of mitochondrial GTP content, putatively leading to hyperactivation of glutamate dehydrogenase. In an independent study, through combined linkage analysis and exome sequencing, we demonstrate in four individuals of two Bedouin Israeli related families the same disease-causing SLC25A36 (NM_018155.3) c.284 + 3A > T homozygous splice-site mutation found in the two siblings. We demonstrate that the mutation, while causing skipping of exon 3, does not abrogate expression of mRNA and protein of the mutant SLC25A36 in patients' blood and fibroblasts. Affected individuals had hyperinsulinism, hyperammonemia, borderline low birth weight, tonic-clonic seizures commencing around 6 months of age, yet normal intellect and no significant other morbidities. Chronic constipation, hypothyroidism, and developmental delay previously described in a single patient were not found. We thus verify that biallelic SLC25A36 mutations indeed cause HI/HA syndrome and clearly delineate the disease phenotype.