Stephen was diagnosed with amyotrophic lateral sclerosis or Lou Gehrig's when he was 21 years old. ALS or Lou Gehrig's is disease which is caused by the nerves that weaken the muscles and makes to work that uses muscles almost impossible to do. You get muscle spasm or weaking of the muscles.
At the age of 24 he completed his doctorate in philosophy.
When Stephen was diagnosed Lou Grieg's disease he started noticing that he was having problem walking so he started using a staff
When Stephen was 27 his health worsen's that led him to use crutches to walk and after sometime he was moved to a wheelchair so can travel around.