May be implicated in endosomal trafficking, or microtubule dynamics, or both. Defects in SPG20 are the cause of spastic paraplegia autosomal recessive type 20 (SPG20); also known as Troyer syndrome (TRS). Spastic paraplegia is a neurodegenerative disorder characterized by a slow, gradual, progressive weakness and spasticity of the lower limbs. Rate of progression and the severity of symptoms are quite variable. Initial symptoms may include difficulty with balance, weakness and stiffness in the legs, muscle spasms, and dragging the toes when walking. In some forms of the disorder, bladder symptoms (such as incontinence) may appear, or the weakness and stiffness may spread to other parts of the body. SPG20 is characterized by dysarthria, distal amyotrophy, mild developmental delay and short stature. Note: This description may include information from UniProtKB.