KIF1A and optic nerve disorder: A likely pathogenic KIF1A p.Ala255Asp variant was identified in a mother and daughter with a complicated HSP phenotype with symptom onset in childhood and additional cerebellar dysfunction (gait ataxia, horizontal and downbeat nystagmus), mild intellectual impairment, optic neuropathy, and a sensorimotor axonal neuropathy with acral leg ulceration.