Conduction in motor evoked potentials correlate with clinical disease severity. In (A) Spastic Paraplegia Rating Scale (SPRS) , in (B) spastic subscore is correlated with central motor conduction time (CMCT) to the right abductor hallucis muscle (AH) (SPRS: r = 0.176; p < 0.028. Spastic subscore: r = 0.241, p < 0.005). Patients with SPG4 mutations are indicated by red triangles, other patients by black squares. Results to the left leg correlated accordingly; data not shown.