In keeping with this, the Drosophila melanogaster ortholog of the HSP gene RTN2 (called RTN-like 1 gene) was found to be required for organization of ER and of distal motor axons, thus supporting the concept that HSP can be caused by axonal ER impairment (O’Sullivan et al. 2012). The gene discussed is HSP90B2P; the disease is hereditary spastic paraplegia.