5. Must have an impaired walking function demonstrated by a mild gait ataxia (Functional System (FS) score = 2 in the cerebellar system component of the EDSS) or a FS score of > 2 in the pyramidal system component of the EDSS based only on evaluation of the lower limbs (hip flexors, knee flexors, knee extensors, and ankle dorsiflexors)or a restricted ambulation (< 1h walking duration) at the Screening Visit.