ERLIN2 and Alzheimer disease: The comparison between AR-SPG18 and AD-SPG18 forms led to the hypothesis that the clinical phenotype of SPG18 may depend on the mode of inheritance, with AD-SPG18 manifesting as a juvenile-adolescent onset pure HSP, whereas AR-SPG18 being a complicated form with earlier onset and more severe course as the likely consequence of a complete loss of function [14].