In this study we confirm that exonic deletion of SPAST is associated with a significant reduction in age at onset of HSP, but show that this reduction is accounted for by a subset of patients in whom the deletion extends into the contiguous gene DPY30. The protein encoded by DPY30 has been implicated in endosome-to-Golgi traffic (Xu et al., 2009). This evidence concerns the gene DPY30 and hereditary spastic paraplegia.