Additionally, nuclear movement of RGCs require microtubule motor proteins such as dynein, and mutations of the tail domain of the heavy chain of cytoplasmic dynein (DYNC1H1) were identified to interrupt the formation and function of the dynein complex, which has been identified as a cause of SMA that has a lower extremity predominance [42,51,52] and of axonal Charcot-Marie-Tooth (CMT) disease [53]. The gene discussed is DYNC1H1; the disease is proximal spinal muscular atrophy.