A rare, complex type of hereditary spastic paraplegia characterized by the onset in childhood/adolescence (ages 2-19) of progressive spastic paraplegia associated mainly with mild to moderate cognitive impairment and developmental delay, cerebellar ataxia, dysarthria, and peripheral neuropathy. Less commonly reported manifestations include skeletal abnormalities (i.e. pes cavus, scoliosis), dyskinesia, dystonia, cataracts, cerebellar signs (i.e. saccadic dysfunction, nystagmus, dysmetria), bladder disturbances, and behavioral problems. SPG26 is caused by mutations in the B4GALNT1 gene (12q13.3), encoding Beta-1, 4 N-acetylgalactosaminyltransferase 1. The disease is MONDO_0012213 (hereditary spastic paraplegia 26). Also known as: GM2 synthase deficiency, SPG26, autosomal recessive spastic paraplegia 26, autosomal recessive spastic paraplegia type 26, hereditary spastic paraplegia type 26.