Mutation in BICD2 has been associated with spinal muscular atrophy, especially in the lower extremity, which is characterized by lower limb muscle weakness and wasting, due to reduced numbers of lumbar motor neurons caused by mutations in DYNC1H1, which encodes a microtubule motor protein in the dynein-dynactin complex and one of its cargo adaptors [80]. Here, DYNC1H1 is linked to proximal spinal muscular atrophy.