Glutamate decarboxylase deficiency
Overview
Glutamate decarboxylase deficiency: A rare disorder of amino acid metabolism characterized by a deficiency of the enzyme called glutamate decarboxylase which causes seizures that will only respond to pyridoxine (vitamin B6).
Symptoms
The list of signs and symptoms mentioned in various sources for Glutamate decarboxylase deficiency includes the 23 symptoms listed below: * Neonatal seizures * Epileptic seizures * Myoclonic seizures * Atonic seizures * Partial seizures * Generalized seizures * Infantile spasms * Abnormal fetal movements * Cognitive impairment * Learning difficulties * Irritability * Abnormal tone * Squinting * Bleeding inside the brain * Abnormal brain myelination * Mental retardation * Psychomotor problems * Speech defect * Reduced muscle tone * Infant respiratory distress * Infant acidosis * Enlarged infant abdomen * Infant vomiting
Causes
* Partial seizure (involve only part of the brain) –Simple (no altered consciousness) –Complex (with altered consciousness) * Generalized seizure (involve both hemispheres) –Tonic-clonic –Atonic –Tonic –Myoclonic –Absence * Epilepsy –Recurrent unprovoked seizures of any or multiple types, which may be idiopathic or symptomatic o Secondary seizure –Metabolic abnormalities (e.g., electrolyte disturbances, hypoglycemia) –Drug effects, intoxication, or withdrawal –Head injury/trauma –Febrile seizures in children –Structural lesions (e.g., tumor, subdural hematoma) –Cerebrovascular etiologies (e.g., cerebral infarct, intracerebral hemorrhage, subarachnoid hemorrhage –Hypoxic-ischemic encephalopathy –Infection (e.g., meningitis, encephalitis) –Hypoxia o Nonepileptic seizure –Not associated with abnormal electrical activity in the brain –Patients with loss of consciousness secondary to cerebral hypoperfusion (fainting, syncope) may occasionally exhibit brief periods of twitching or convulsive movements resembling seizure activity –Psychological disturbances (pseudoseizure) o Inborn errors of metabolism –Disorders of amino acid metabolism –Organic acidemias –Urea cycle disorders –Mitochondrial disorders –Peroxisomal disorders –Glycogen storage disorders –Disorders of sugar metabolism o Rasmussen's encephalitis –Causes seizures and progressive hemispheric dysfunction in infants
Diagnosis
If you suspect a patient is having an absence seizure, evaluate its occurrence and duration by reciting a series of numbers and then asking him to repeat them after the attack ends. If the patient has had an absence seizure, he can’t do this. Alternatively, if the seizures are occurring within minutes of each other, ask the patient to count for about 5 minutes. He’ll stop counting during a seizure and resume when it’s over. Look for accompanying automatisms. Find out if the family has noticed a change in behavior or deteriorating schoolwork.
Treatment
* Generalized status epilepticus (continuous or recurrent seizure activity without a return to baseline for >30 minutes) is a medical emergency and should be treated aggressively with IV antiepileptic medications * Remove offending intoxicants or medications * Correct metabolic abnormalities as necessary * Numerous anticonvulsant medications are available for acute and chronic use –Select the most appropriate agent on the basis of the clinical situation, seizure type, and side effect profile –Combination anticonvulsant therapy may be effective for patients refractory to a single agent * Vagus nerve stimulators are effective in patients refractory to anticonvulsant therapy * Epilepsy surgery also may be effective in controlling seizures in carefully selected surgical candidates who are refractory to chronic anticonvulsant medication * Lifestyle modification and avoidance of triggers (e.g., sleep deprivation, alcohol)