Background

Amyotrophic lateral sclerosis (ALS) is a heterogeneous neurodegenerative disease caused by loss of the upper motor neurons, i.e. neurons that extend from the cortex to the brain stem and the spinal cord, and lower motor neurons, i.e. neurons that connect the brainstem or spinal cord to muscle (Hardiman et al. 2017). Progressive loss of these neuron populations precede into two distinct early presentation of ALS symptoms: patients diagnosed with spinal-onset display a significant weakness of the limbs whereas bulbar-onset leads to difficulty swallowing (dysphagia) and difficulty speaking (dysarthria) (Hardiman et al. 2017). As the disease progresses, symptoms converge and death due to respiratory failure usually occurs within 3-5 years. ALS can also be grouped as either sporadic ALS (sALS),