\Amyotrophic lateral sclerosis protein 2 (ALS2) or Alsin is a 184kD protein that contains three guanine-nucleotide exchange factor domains and may act as a GTPase regulator. ALS2 dysfunction affects endosome trafficking through a Rab5 small GTPases family-mediated mechanism. It is a causative gene for a juvenile autosomal recessive form of motor neuron diseases, including amyotrophic lateral sclerosis 2. This disorder is characterized by a progressive degeneration of the upper motor neurons of the motor cortex and the lower motor neurons of the brain stem and spinal cord.