Epilepsy in succinic semialdehyde dehydrogenase deficiency, a disorder of GABA metabolism

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Objectives: Succinic semialdehyde dehydrogenase (SSADH) deficiency is a gamma-aminobutyric acid (GABA) degradative defect. Epilepsy affects half of patients. The murine model is associated with a transition from absence to convulsive seizures in the third week, with fatal status epilepticus. Methods: The clinical phenotype is reported from a patient database. Flumazenil-Positron Emission Topography (FMZ-PET) and Transcranial Magnetic Stimulation (TMS) were used to study GABA neurotransmission. Electrocorticography, single cell electrophysiology, and radioligand binding studies are reported from animal studies. Results: Generalized seizures predominate, including tonic-clonic, atypical absence, and myoclonic. EEG discharges are typically generalized spike-wave. MRI shows a dentatopallidoluysian pattern. Sudden Unexpected Death in Epilepsy Patients (SUDEP) has occurred and the associated neuropathology reveals chronic excitotoxic injury in gloubus pallidus. Investigations using FMZ-PET and TMS support downregulation of GABA A and GABA B activity, respectively, in patients. Gamma-hydroxybutyrate (GHB) induces spike-wave discharges in homozygous null mice via GHB and GABA B-mediated mechanisms. These resemble absence seizures and are abolished by a GABA B receptor antagonist. Decreased binding of GABA A and GABA B receptor antagonists has been demonstrated in P19 and P14 null mice, respectively. Downregulation of GABA A and GABA B receptor subunits is observed by P14. GABA A and GABA B mediated potentials are reduced from P8-P14. Conclusion: Generalized epilepsy and epileptiform discharges are characteristic of SSADH deficiency. Spontaneous absence seizures appear in null mice by the third week, which may be induced by GHB or GABA B activity. Subsequent overuse dependent downregulation of GABA A and GABA B receptor activity may be associated with hyperexcitability concomitant with the transition to generalized seizures. © 2011 The Japanese Society of Child Neurology.

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Brain and Development