Genetic mutations in the human DP1 protein REEP1 that are associated with autosomal dominant hereditary spastic paraplegia type 31 (SPG31) [11–17] and distal hereditary motor neuropathy type V (dHMN5) [18] are found at this dimer interface [19,20]. The gene discussed is REEP1; the disease is hereditary spastic paraplegia 31.