“Hereditary spastic paraplegia” (HSP) is a clinical diagnostic designation for those neurologic syndromes a) in which bilateral lower extremity weakness and spasticity (each of variable degree) are the predominant (but often not only) manifestations; and b) for which gene mutation is the major causative factor. As with all classifications of clinical syndromes, it may be problematic to decide if a given disorder should be included or excluded in the category of HSP. For example, whereas paraplegin gene mutation, in which spastic paraparesis is often associated with ataxia, is recognized as a form of HSP (SPG7), Friedreich's ataxia and Charlevoix-Saguenay, syndromes in which ataxia is often associated with corticospinal tract deficits are considered forms of spinocerebellar ataxia and not forms of HSP. Although distal axon degeneration of corticospinal tracts is often reported in post mortem examination of HSP (discussed below), classification of a given clinico-genetic syndrome as a form of HSP is based on clinical and genetic features rather than neuropathologic features