Monarch Disease Ontology entry MONDO_0012453 (hereditary spastic paraplegia 31) is a rare type of hereditary spastic paraplegia usually characterized by a pure phenotype of proximal weakness of the lower extremities with spastic gait and brisk reflexes, with a bimodal age of onset of either childhood or adulthood (>30 years). In some cases, it can present as a complex phenotype with additional associated manifestations including peripheral neuropathy, bulbar palsy (with dysarthria and dysphagia), distal amyotrophy, and impaired distal vibration sense. Also known as: REEP1 hereditary spastic paraplegia, SPG31, autosomal dominant spastic paraplegia 31, autosomal dominant spastic paraplegia type 31, hereditary spastic paraplegia caused by mutation in REEP1, hereditary spastic paraplegia type 31.