ELP1 and amyotrophic lateral sclerosis: To determine whether the apparent depletion of nucleolar TDP-43 in Elp1 CKOs might reflect the diminishing size of alpha motor neurons and a proportionate decrease in nucleolar size, rather than a true loss of TDP-43 production or stability, we quantified the level of TDP-43 per unit area in large (≥ 440 μm2), CHAT-positive neurons, a primary cell type impacted in ALS.