The Spastic Paraplegia Foundation is dedicated to advancing research and ultimately developing cures for two groups of closely related upper motor neuron disorders called Primary Lateral Sclerosis (PLS) and Hereditary Spastic Paraplegia (HSP). 

These conditions share the common feature of degeneration of long motor nerves called upper motor neurons. These nerves begin in the motor cortex of the brain and extend down the spinal cord. HSP and PLS can be referred to as "primary upper motor neuron disorders" because there is little, if any, lower motor neuron involvement. See What's Happening.

In both disorders, this degeneration causes the progressive loss of the use of the legs. In PLS, the arms, speech and swallowing as well as the legs are affected, usually over the period of a few years. In rare forms of HSP, there are additional neurological symptoms as well.

The disorder name "Hereditary Spastic Paraplegia" describes the symptoms of the disease. HSP is Heredity and it's symptoms are Spasticity and Paraplegia.

The disorder name "Primary Lateral Sclerosis" describes the disease process, rather than the symptoms. Degeneration occurs: Primarily in the Lateral columns of the spinal cord. Sclerosis means "scarring".

The primary degenerative process in both groups of disorders occurs in the lateral columns, also called the cortico-spinal tracts. The symptoms of both conditions are increasing spasticity and weakness of the affected muscles. Brain neurons appear to also be affected in PLS, and, in some forms of HSP, as well.

The SPF is dedicated to conquering these two groups of upper motor neuron disorders.