Phase 2 Clinical Trial of SGS-742 Therapy in Succinic Semialdehyde Dehydrogenase Deficiency

Objective: To perform a clinical trial assessing the safety, tolerability and efficacy of the GABA(B) receptor antagonist SGS-742 in patients with SSADH deficiency. Study Population: Twenty-two children and adults with SSADH deficiency. Design: Double-blind, cross-over, phase II clinical trial. SGS-742 is a GABA (B) receptor antagonist that has shown to be safe and well-tolerated in clinical trials in adults with cognitive impairment. In addition, preliminary data in the SSADH knockout mouse model suggest efficacy in this specific syndrome. The primary outcome measure will be a change in the Auditory Comprehension subtest of the Neuropsychological Assessment Battery Language Module score; the secondary outcome measure will be a change in cortical excitation and inhibition measured by transcranial magnetic stimulation (TMS). Additional evaluations will include neurological and neuropsychological examinations, magnetic resonance spectroscopy and CSF collection to measure GABA levels. The trial will have a baseline phase in which each patient will undergo a neurological examination and a neuropsychological evaluation. During the subsequent treatment phase, patients will be randomized to SGS-742, supplied by IRIX Pharmaceuticals, and based on weight given a maximum tolerated dose not to exceed 600 mg t.i.d. orally, or placebo, each for 6 months. Patients will then have repeat TMS, neurological and neuropsychological evaluations, followed by cross-over to the alternate treatment arm, and re-evaluation after 6 months. Outcome Measures: The primary outcome measures for drug efficacy will be performance on neuropsychological testing and responses to parent questionnaire. The secondary outcome measure will be TMS parameters of cortical excitation and inhibition. The outcome measures for safety will include clinical examination and neuropsychological tests.