Symptoms may also be affected by environment, nutrition, general health of the patient, other genetic mutations, and additional factors that are not yet understood. The number of symptoms and the severity of them can vary greatly from one person to the next, even within the same family. Some people have few symptoms, with only a mildly affected gait, while others are affected more severely, to the point of needing a wheelchair. There is no way to accurately predict what one symptoms an individual will have, or how severe they will be. One of the identifying features of Hereditary Spastic Paraplegia is that it has gone through a stage of progression at some point, which can help distinguish it from non-progressive disorders such as Cerebral Palsy.
Progression can stop after a number of years, or can continue throughout life.
For some people, symptoms begin in early childhood and stop progressing after adolescence. Some people find that their symptoms worsen when they are angry, stressed, or upset. Even among people without HSP, stress can cause a tightening of the muscles. For people with HSP, that phenomenon may be greatly magnified. It is unknown exactly how emotions affect muscle tone, but it may involve adrenalin levels.