OPTN and amyotrophic lateral sclerosis: Lastly, there is a rare mutation that involves a 2 base pair (bp) insertion into exon 6 of the OPTN gene (691_692insAG or 2bpIns-OPTN) that is associated with NTG and amyotrophic lateral sclerosis (ALS) (Medchalmi et al., 2021).