Three different SOD-1 mutations were present in the patients studied: GTA-to-GGA sequence change resulting in valine to glycine substitution in exon 5 at the 148 position (V148G), GAA-to-GGA sequence change resulting in a glutamic acid-to-glycine substitution in exon 4 at the 100 position (E100G), and ATT-to-ACT sequence change resulting in an isoleucine to threonine substitution in exon 4 at the 113 position (I113T). The site of disease onset was classified as upper limb (UL), lower limb (LL) or bulbar (B). Disease duration refers to the period from symptom onset to date of testing. The patients were clinically graded using the amyotrophic lateral sclerosis functional rating scale—revised (ALSFRS-R), with a maximum score of 48 when there is no disability. Muscle strength was clinically assessed using the Medical Research Council for the abductor pollicis brevis, as this muscle was utilised for excitability testing. Data for 45 sporadic amyotrophic lateral sclerosis (SALS) patients (32 males and 13 females) are also presented for comparison. Twenty-five amyotrophic lateral sclerosis (ALS) patients reported upper-limb onset, 10 lower limb and 10 bulbar disease onset.

↵* Underwent cortical excitability studies.

F, female; M, male.