Early Presentation of Hyperinsulinism/Hyperammonemia Syndrome in Three Serbian Patients

Evolutionary Changes in Primate Glutamate Dehydrogenases 1 and 2 Influence the Protein Regulation by Ligands, Targeting and Posttranslational Modifications

There are two paralogs of glutamate dehydrogenase (GDH) in humans encoded by the GLUD1 and GLUD2 genes as a result of a recent retroposition during the evolution of primates. The two human GDHs possess significantly different regulation by allosteric ligands, which is not fully characterized at the structural level. Recent advances in identification of the GDH ligand binding sites provide a deeper perspective on the significance of the accumulated substitutions within the two GDH paralogs. In this review, we describe the evolution of GLUD1 and GLUD2 after the duplication event in primates using the accumulated sequencing and structural data. A new gibbon GLUD2 sequence questions the indispensability of ancestral R496S and G509A mutations for GLUD2 irresponsiveness to GTP, providing an alternative with potentially similar regulatory features. The data of both GLUD1 and GLUD2 evolution not only confirm substitutions enhancing GLUD2 mitochondrial targeting, but also reveal a conserved mutation in ape GLUD1 mitochondrial targeting sequence that likely reduces its transport to mitochondria. Moreover, the information of GDH interactors, posttranslational modification and subcellular localization are provided for better understanding of the GDH mutations. Medically significant point mutations causing deregulation of GDH are considered from the structural and regulatory point of view.

Glutamate dehydrogenase hyperinsulinism: mechanisms, diagnosis, and treatment

Congenital hyperinsulinism (CHI) is a genetically heterogeneous disease, in which intractable, persistent hypoglycemia is induced by excessive insulin secretion and increased serum insulin concentration. To date,15 genes have been found to be associated with the pathogenesis of CHI. Glutamate dehydrogenase hyperinsulinism (GDH-HI) is the second most common type of CHI and is caused by mutations in the glutamate dehydrogenase 1 gene. The objective of this review is to summarize the genetic mechanisms, diagnosis and treatment progress of GDH-HI. Early diagnosis and treatment are extremely important to prevent long-term neurological complications in children with GDH-HI.

Clinical and genetic characteristics of patients with congenital hyperinsulinism in 21 non-consanguineous families from Serbia

Persistent hypoglycaemia in newborns and infants is most commonly caused by congenital hyperinsulinism (CHI). Most CHI studies report outcomes in children from both consanguineous and non-consanguineous families which can affect the phenotype-genotype analysis. The aim of this study was to analyze characteristics of patients with CHI in 21 non-consanguineous families from Serbia. This retrospective cohort study included a total of 21 patients with CHI treated in the Mother and Child Healthcare Institute of Serbia during the past 20 years. The prevalence of macrosomia at birth was very low in our cohort (4.8%). Median age at presentation was 6 days, with seizures as the presenting symptom in 76% of patients. Only four patients (19%) were diazoxide unresponsive, and eventually underwent pancreatectomy. Genetic testing was performed in 15 patients and genetic diagnosis was confirmed in 60%, with all patients being heterozygous for detected mutations. The ABCC8 gene mutations were detected in 55.6%, GLUD1 in three patients (33.3%) with HIHA syndrome and one patient had HNF4A gene mutation and unusual prolonged hyperglycaemia lasting 6 days after diazoxide cessation. Neurodevelopmental deficits persisted in 33% of patients.Conclusion: This is the first study regarding CHI patients in Serbia. It suggests that in countries with low consanguinity rate, majority of CHI patients are diazoxide responsive. The most common mutations were heterozygous ABCC8, followed by GLUD1 and HNF4A mutations, suggesting the potential benefit of population-tailored genetic analysis approach, targeting the mutations causing CHI via dominant inheritance model in regions with low consanguinity rates. What is Known: • Persistent hypoglycaemia during infancy and early childhood is most commonly caused by congenital hyperinsulinism (CHI). • Consanguinity is a very important factor regarding the genetics and phenotype of CHI, increasing the risk of autosomal recessive genetic disorders, including the severe, diazoxide-unresponsive forms caused by recessive inactivating mutations in ABCC8 and KCNJ11. What is New: • Results of the present study which included CHI patients from 21 non-consanguineous families suggest that in countries with low consanguinity rates, majority of CHI patients can be diazoxide responsive, with most common mutations being heterozygous ABCC8, followed by GLUD1 and HNF4A mutations. • Unusually prolonged hyperglycaemic reaction to diazoxide treatment in a patient with HNF4A mutation was also described in the present study.

Hyperinsulinism-hyperammonemia Syndrome in an Infant with Seizures

Hyperinsulinism-hyperammonemia syndrome (HI/HA) is the second most common form of persistent hyperinsulinemic hypoglycemia of infancy (PHHI). The main clinical characteristics of HI/HA syndrome are repeated episodes of symptomatic hypoglycemia, but not usually severe. Consequently, children with HI/HA syndrome are frequently not recognized in the first months of life. An 8-month-old boy was admitted to a hospital due to hypoglycemia seizures. He also had asymptomatic hyperammonemia with no signs of lethargy or headaches. Genetic testing revealed autosomal dominant syndrome, a mutation in the GLUD1 gene (p.Arg274Cys). The boy started treatment with diazoxide. Subsequent growth and neurological development were normal. Hypoglycemic symptoms in HI/HA syndrome may vary from being non specific to severe. As hypoglycemia could lead to brain injury and impairment of neurological development, timely diagnosis and management are essential. If transient hypoglycemia is ruled out, metabolic disorders must be taken into account.

Diagnosis and treatment of hyperinsulinaemic hypoglycaemia and its implications for paediatric endocrinology

Glucose homeostasis requires appropriate and synchronous coordination of metabolic events and hormonal activities to keep plasma glucose concentrations in a narrow range of 3.5–5.5 mmol/L. Insulin, the only glucose lowering hormone secreted from pancreatic β-cells, plays the key role in glucose homeostasis. Insulin release from pancreatic β-cells is mainly regulated by intracellular ATP-generating metabolic pathways. Hyperinsulinaemic hypoglycaemia (HH), the most common cause of severe and persistent hypoglycaemia in neonates and children, is the inappropriate secretion of insulin which occurs despite low plasma glucose levels leading to severe and persistent hypoketotic hypoglycaemia. Mutations in 12 different key genes (ABCC8, KCNJ11, GLUD1, GCK, HADH, SLC16A1, UCP2, HNF4A, HNF1A, HK1, PGM1 and PMM2) constitute the underlying molecular mechanisms of congenital HH. Since insulin supressess ketogenesis, the alternative energy source to the brain, a prompt diagnosis and immediate management of HH is essential to avoid irreversible hypoglycaemic brain damage in children. Advances in molecular genetics, imaging methods (¹⁸F–DOPA PET-CT), medical therapy and surgical approach (laparoscopic and open pancreatectomy) have changed the management and improved the outcome of patients with HH. This up to date review article provides a background to the diagnosis, molecular genetics, recent advances and therapeutic options in the field of HH in children.