The hereditary spastic paraplegias are a group of clinically and genetically diverse disorders characterized by progressive, usually severe, lower extremity spasticity. They are classified based on their mode of inheritance and whether they are uncomplicated (isolated spasticity) or complicated (occurs with other neurologic abnormalities including optic neuropathy, retinopathy, extrapyramidal disturbance, dementia, ataxia, ichthyosis, mental retardation, and deafness)