Novel missense mutations outside the allosteric domain of glutamate dehydrogenase are prevalent in European patients with the congenital hyperinsulinism-hyperammonemia syndrome.
ABSTRACT The hyperinsulinism-hyperammonemia syndrome (HHS) has been shown to result from 'gain-of-function' mutations of the glutamate dehydrogenase (GlDH) gene, GLUD1. In the original report, all mutations were found in a narrow range of 27 base pairs within exons 11 and 12 which predicted an effect on the presumed allosteric domain of the enzyme and all these mutations were associated by a diminished inhibitory effect of guanosine triphosphate (GTP) on GlDH activity. We have investigated 14 patients from seven European families with mild hyperinsulinism. In four families, more than one member was affected. In eight cases hyperammonemia was documented, and eight cases had signs of significant leucine sensitivity. In one of the families, a novel heterozygous missense mutation in exon 6 [c.833C>T (R221C)] was detected, and in all other cases from six unrelated families the novel heterozygous missense mutation c.978G>A (R269H) was found in exon 7. When GIDH activity was measured in lymphocytes isolated from affected patients, both mutations were shown to result in a normal basal activity but a diminished sensitivity to GTP. It is the first time that this effect is reported for mutations located in the presumed catalytic site and outside the GTP allosteric domain of the enzyme. The observation of the high prevalence of the exon 7 mutation both in familial and sporadic cases of HHS suggests a mutation hot spot and justifies a mutation screening for this novel mutation by mismatch PCR-based restriction enzyme digestion in patients with hyperinsulinism.
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ABSTRACT: An increased concentration of ammonia is a non-specific laboratory sign indicating the presence of potentially toxic free ammonia that is not normally removed. This does occur in many different conditions for which hyperammonemia is a surrogate marker. Hyperammonemia can occur due to increased production or impaired detoxification of ammonia and should, if associated with clinical symptoms, be regarded as an emergency. The conditions can be classified into primary or secondary hyperammonemias depending on the underlying pathophysiology. If the urea cycle is directly affected by a defect of any of the involved enzymes or transporters, this results in primary hyperammonemia. If however the function of the urea cycle is inhibited by toxic metabolites or by substrate deficiencies, the situation is described as secondary hyperammonemia. For removal of ammonia, mammals require the action of glutamine synthetase in addition to the urea cycle, in order to ensure lowering of plasma ammonia concentrations to the normal range. Independent of its etiology, hyperammonemia may result in irreversible brain damage if not treated early and thoroughly. Thus, early recognition of a hyperammonemic state and immediate initiation of the specific management are of utmost importance. The main prognostic factors are, irrespective of the underlying cause, the duration of the hyperammonemic coma and the extent of ammonia accumulation. This paper will discuss the biochemical background of primary and secondary hyperammonemia and will give an overview of the various underlying conditions including a brief clinical outline and information on the genetic backgrounds.Archives of Biochemistry and Biophysics 04/2013; · 3.37 Impact Factor
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ABSTRACT: Objective: Hyperinsulinemic hypoglycemia (HIH) is a genetically heterogeneous disorder with both familial and sporadic variants. Patients with HIH may present during the neonatal period, infancy, or childhood and may show transient, prolonged, and persistent features. In this study, we aimed to discuss our experience with HIH patients, based on a series of 17 patients.Methods: We retrospectively analyzed the clinical and laboratory characteristics at the time of diagnosis and during treatment and evaluated the neurodevelopmental outcomes during follow-up in 17 HIH patients, who presented or were referred to the Pediatric Endocrinology Clinic of Dr. Sami Ulus Training and Research Children's Hospital between 1998 and 2011. The patients (7 male, 10 female) were aged between the first day of life and 7 years - 10 were in their first week of life, 6 in their infancy, and 1 in childhood.Results: None of the mothers had gestational diabetes. Hypoglycemic seizure (76.5%) was the most common presenting symptom. Medical treatment failed in two patients, and was stopped in eight patients. Of two diazoxide-unresponsive patients, one underwent near-total pancreatectomy, but hypoglycaemic episodes continued after surgery. The parents of other patient refused surgery, the medical treatment was continued, nevertheless, severe motor and mental retardation developed. At follow-up, 23.5% of the patients were found to have mild or moderate psychomotor retardation, and 23.5% developed epilepsy. There was no marked difference in neurological results between cases with onset in the neonatal period or in infancy.Conclusions: Clinical course and treatment response in HIH cases are very heterogeneous. Long-term careful monitoring is needed to detect and treat the complications.Journal of Clinical Research in Pediatric Endocrinology 09/2013; 5(3):150-5.
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ABSTRACT: Congenital hyperinsulinism (CHI) is a genetic disorder characterized by profound hypoglycaemia related to an inappropriate insulin secretion. It is a heterogeneous disease classified into two major subgroups: "channelopathies" due to defects in ATP-sensitive potassium channel, encoded by ABCC8 and KCNJ11 genes, and "metabolopathies" caused by mutation of several genes (GLUD1, GCK, HADH, SLC16A1, HNF4A and HNF1A) and involved in different metabolic pathways. To elucidate the genetic aetiology of CHI in the Italian population, we conducted an extensive sequencing analysis of the CHI-related genes in a large cohort of 36 patients: Twenty-nine suffering from classic hyperinsulinism (HI) and seven from hyperinsulinism-hyperammonemia (HI/HA). Seventeen mutations have been found in fifteen HI patients and five mutations in five HI/HA patients. Our data confirm the major role of ATP-sensitive potassium channel in the pathogenesis of Italian cases (~70%) while the remaining percentage should be attributed to other. A better knowledge of molecular basis of CHI would lead to improve strategies for genetic screening and prenatal diagnosis. Moreover, genetic analysis might also help to distinguish the two histopathological forms of CHI, which would lead to a clear improvement in the treatment and in genetic counseling.Gene 03/2013; · 2.20 Impact Factor