Succinic semialdehyde dehydrogenase (SSADH) deficiency is an autosomal recessive disease involving the catabolism of the neurotransmitter γ-amino-butyric acid (GABA). The main symptoms include retardation of psychomotor and language development, muscle hypotonia and non-progressive ataxia. Therapy consisting of approximately 75 mg/kg per day of vigabatrin, an irreversible inhibitor of GABA-transaminase, is reported to lead to some improvement of the clinical condition in affected patients. We report on a 12-year-old boy with SSADH deficiency who, when treated with 75 mg/kg per day of vigabatrin, showed marked amelioration of symptoms but also EEG changes and two generalized seizures. On discontinuing vigabatrin therapy, the seizures resolved and the EEG improved, but the patient's clinical condition deteriorated to its pre-treatment state. A stable EEG without the recurrence of seizures as well as renewed improvement of cognitive and behavioural functions was achieved with a reduced vigabatrin dose of 25 mg/kg per day. We conclude that vigabatrin in SSADH deficiency should be administered in a gradually increasing dosage combined with frequent evaluation of the clinical condition and the EEG.
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