TARDBP and amyotrophic lateral sclerosis: The above data demonstrated that expression of WT or ALS-associated mutant human TDP-43 markedly affects cell viability and growth in yeast strains carrying two or more copies of the transgene, while the expression of TDP-43 (either WT or mutated) from a single genomic copy was not sufficient to cause cell death, pointing to a saturating effect of two transgene copies for TDP-43 cytotoxicity.