More recently, mutations in two other ER-shaping protein families have been identified to cause rare forms of HSP: reticulon-2 (RTN2) has been linked to SPG1216 and ADP-ribosylation factor-like 6 interacting protein 1 (ARL6IP1) has been linked to SPG6117. The gene discussed is ARL6IP1; the disease is hereditary spastic paraplegia.