SPG31 is an HSP caused by pathogenic variants in the REEP1 gene and codes the receptor expression-enhancing protein-1 (REEP1), which is involved in mitochondrial and endoplasmic reticulum (ER) protein processing and transport in motor neurons in the spinal cord and brain (de Souza et al., 2017). Here, REEP1 is linked to hereditary spastic paraplegia.