One possibility isthat the HSP-SPG4 patients described with late-life dementia could in fact also havea coincidental, more common disease, such as Alzheimer's or Vascular Dementia.Another hypothesis is that SPG4 mutations might act as a riskfactor that can, in association with other elements, trigger multifactorialdegenerative dementias. Here, SPAST is linked to vascular dementia.