HTT and proximal spinal muscular atrophy: Spinal muscular atrophy (SMA) is caused by deletion or mutations in survival of motor neuron 1 (SMN1), amyotrophic lateral sclerosis (ALS) is caused by mutations in superoxide dismutase 1 (SOD1), TAR DNA binding protein (TARDBP), fused in sarcoma (FUS/TLS), or other genes and Huntington's disease is caused by an expansion of CAG repeats in Huntingtin (Ule, 2008).