SYN1 and amyotrophic lateral sclerosis: For example, C9orf72 has been shown to interact with the presynaptic protein, Synapsin-I, and perturbed interactions between C9orf72 and Synapsin-I in ALS may be associated with excitatory synapse dysfunction and loss (Devlin et al., 2015; Perkins et al., 2021; Bauer et al., 2022).