KIF1B, or kinesin-like protein (Klp) functions as a motor for mitochondrial transport, and has a microtubule plus end-directed motility. The KIF1B beta isoform is abundant in brain, while the alpha isoform is abundant in skeletal muscle. Mutations in the KIF1B gene are the cause of Charcot-Marie-Tooth disease type 2A1, which is a primary peripheral axon neuropathy. The KIF1B beta isoform is down-regulated in sporadic amyotrophic lateral sclerosis (ALS).