If mitochondria are unable to counterbalancecell dysfunction, a secondary mitochondrial disease, such as ALS caused by amutation in trans-activation response DNA-binding protein 43 (TDP-43) [29], canalso occur in spinal muscular atrophy (usually caused by a mutation in the codingsequence of survival of motor neuron 1) [30]. The gene discussed is TARDBP; the disease is proximal spinal muscular atrophy.