Nonketotic hyperglycinemia (NKH) is an autosomal recessive disorder due to a fundamental defect in the glycine cleavage system, which leads to neuronal dysfunction caused by two receptor-mediated mechanisms. It is a life-threatening condition in the neonate. Until now, the disease has not been described from Saudi Arabia. We report on three Saudi newborns (two males and one female) who had NKH. Two of these were siblings (male and female). Following uneventful deliveries, they presented between the first and third day of life with progressive lethargy, poor feeding, recurrent apnea and severe hypotonia. Two newborns had myoclonic seizures, whereas electroencephalogram showed burst-suppression pattern in all of them. The diagnosis was confirmed by high cerebrospinal fluid/plasma glycine ratio (0.2 and 1.08) in two patients (normal < 0.030, whereas a sibling of one of the neonates had a high glycine level. Both siblings died during the second month of life despite therapy with dextromethorphan (an N-methyl-D-asparate [NMDA] receptor antagonist) in one of them. The third day had ketamine (noncompetitive NMDA receptor antagonist) and sodium benzoate (that conjugates with glycine, forming nontoxic hippuric acid). Although his seizures were controlled, he survived with severe neurological sequelae.
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Nonketotic hyperglycinemia (NKH), also known as glycine encephalopathy, is a rare inherited neurometabolic disorder caused by a deficiency in the glycine cleavage enzyme system (GCS), leading to the pathological accumulation of glycine in blood and cerebrospinal fluid (CSF). This case report details a neonate presenting with central apnea, profound hypotonia, and refractory seizures, alongside prenatal findings of polyhydramnios and hiccup-like fetal movements, all strongly suggestive of severe NKH. Diagnostic evaluation confirmed markedly elevated glycine levels in serum and CSF, with a CSF-to-plasma glycine ratio exceeding 0.
View Article and Find Full Text PDFAnesthetic management using desflurane and nitrous oxide in a child with non-ketotic hyperglycinemia: a case report.
JA Clin Rep
December 2024
Department of Anesthesiology, Niigata University Medical and Dental Hospital, 1-754 Asahimachi-Dori, Chuo-Ku, Niigata, 951-8520, Japan.
Background: Non-ketotic hyperglycinemia (NKH) is a rare autosomal recessive disorder caused by defects in the glycine cleavage system, leading to elevated glycine levels in the central nervous system. NKH manifests in various forms, with the neonatal type being the most severe and often associated with high mortality and significant neurological impairment. This case report highlights the successful uses of desflurane and nitrous oxide for anesthetic management in a patient with NKH.
View Article and Find Full Text PDFThe role of NMDA-receptor type glutamatergic antagonists dextromethorphan or ketamine in the treatment of nonketotic hyperglycinemia: A critical reassessment.
Mol Genet Metab
November 2024
Department of Pediatrics, Section of Clinical Genetics and Metabolism, University of Colorado, Aurora, CO 80045, USA. Electronic address:
The recognition of glycine as an endogenous ligand at the allosteric activation site of the NMDA-type glutamatergic receptor led to the assumption that the excess glycine in nonketotic hyperglycinemia would result in overactivation of these receptors, and of the proposed use of inhibitors such as dextromethorphan or ketamine as a therapeutic agent. Years later it was recognized that these same receptors have an alternative endogenous activator d-serine, which is markedly decreased in nonketotic hyperglycinemia. This may result in underactivation of these NMDA-type glutamatergic receptors, challenging the earlier hypothesis.
View Article and Find Full Text PDFCase report: Unveiling genetic and phenotypic variability in Nonketotic hyperglycinemia: an atypical early onset case associated with a novel variant.
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Service de Neurologie Pédiatrique, CHU Bordeaux, University Bordeaux, CNRS, INCIA, UMR 5287, NRGen Team, Bordeaux, France.
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- * A new case of NKH was identified involving a child with a unique genetic variant in the GLRX5 gene that led to significant neurological problems, confirmed through MRI and cerebrospinal fluid analysis.
- * The child, who experienced a rapid decline in health, passed away at four months old, demonstrating that this case was more severe than previously documented instances of GLRX5-related NKH, emphasizing the importance of genetic factors in the disorder's severity and symptoms.
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