1. A method for diagnosing the presence of SPG8-associated hereditary spastic paraplegia (HSP) or predicting the risk of developing SPG8-associated HSP in a human subject, comprising, a) obtaining a nucleic acid sample from a subject suspected of having HSP or being at risk of developing HSP; and b) determining the presence or absence of a nucleotide sequence defect in all or a portion of, a nucleic acid sequence encoding a polypeptide consisting of the sequence of SEQ ID NO: 19 in the nucleic acid sample obtained from the subject; wherein the defect is a missense mutation, a splice site mutation, a nonsense mutation, an insertion, a deletion or a frameshift mutation; wherein the mutation causes a disruption of the function or conformation of the encoded protein, or decreased expression or absence of the encoded protein; and wherein detection of a sequence defect is indicative that the subject has or is at risk of developing SPG8-associated HSP.