 This is the first-time-in-human FTIH phase IIIa study of GSK1223249, a humanised monoclonal antibody against Nogo-A, a neurite outgrowth inhibitor hypothesised to be involved in the pathophysiology of amyotrophic lateral sclerosis ALS and some other neurodegenerative disorders. This study will be a randomized, placebo-controlled, double-blind, sequential dose escalation, 2-part fusion protocol. Approximately 76 patients with ALS will be enrolled. In Part 1, single escalating intravenous i.v. doses of GSK1223249 are planned to be evaluated in 5 sequential patient cohorts 2 placebo and 6 active in each cohort to determine single dose safety and pharmacokinetics PK. Part 2 will also be of a sequential dose escalating design, but patients in each of the planned 3 cohorts 3 placebo, 9 active in each cohort will receive 2 repeat i.v. doses approximately 4 weeks apart where, safety and PK will also be evaluated. In two cohorts in Part 1 and all cohorts in Part 2, blood samples and skeletal muscle biopsies will be taken from patients before and at the end of treatment to demonstrate whether or not GSK1223249 binds to its target and produces any measurable pharmacodynamic effect. Patients in both parts will receive their first dose in a hospital-based unit where they will be monitored for at least 24 hours post-dose before being discharged to be followed on an out-patient basis. In each cohort in part 1, the first four subjects will be dosed in a staggered manner such that only one will receive the dose in any 24 hours. Dosing of the first four subjects in the first cohort of part 2 will also be staggered in a similar manner. 