KIF1C and Global developmental delay: For example, all patients with SPG10 and SPG21 presented initially with spasticity and gait disturbance; developmental delay (55.6%) was the initial manifestation in most individuals with SPG20; the only genotypes in which tremor was reported as the initial presenting symptom were SPG11, SPG46, and SPG58, yet SPG11 was the commonest genotype among those who initially manifested with tremor (76.9%) and mental disorders (76.0%).