ARL6IP1 and hereditary spastic paraplegia: Arl6IP1 and protrudin are also known as SPG (spastic paraplegias) 61 and SPG33, respectively, because hereditary spastic paraplegias, a group of inherited neurological disorders whose pathology is characterized by axonal degeneration of corticospinal motor neurons, is caused by pathogenic mutations in Arl6IP1 and Protrudin genes (35, 36, 37, 38).