The present invention relates to a mutant human alpha-synuclein with increased toxicity compared to wild-type alpha-synuclein, or a homologue thereof, wherein the mutant alpha-synuclein or homologue thereof comprises at least one amino acid substitution selected from the group consisting of a substitution at the alanine at position 56 (A56), at the alanine at position 76 (A76), at the methionine at position 127 (M127) and/or at the valine at position 118 (V118), as defined in the claims. Further, the invention relates to a polynucleotide encoding the mutant alpha-synuclein or homologue thereof, or an expression vector comprising said polynucleotide, a cell comprising the polynucleotide or expression vector, as defined in the claims. Also, a non-human animal comprising the cell of the invention is provided, as defined in the claims. Finally, the invention provides methods for identifying a substance that prevents or reduces toxicity of alpha-synuclein, as defined in the claims.