TTN and amyotrophic lateral sclerosis: Human primary SkMS contained a heterogenous population of mature and differentiating skeletal muscle cells, confirmed by expression of MYOD (myoblast progenitor), TITIN (intermediate filament marker) and FMHC – a marker for fast fatigable skeletal muscle fibres and the muscle cell type primarily affected in ALS (Mukund and Subramaniam 2020; Schweingruber and Hedlund 2022) (Supplemental Fig. 1G, G’).