docs: def _add_vertex_attributes(self, genes: List[Gene],
                                 disease_associations: Optional[dict] = None) -> None:
          """Add attributes to vertices.
  
          :param genes: A list of genes containing attribute information.
          """
          self._set_default_vertex_attributes()
          self._add_vertex_attributes_by_genes(genes)
  
          # compute up-regulated and down-regulated genes
          up_regulated = self.get_upregulated_genes()
          down_regulated = self.get_downregulated_genes()
  
          # set the attributes for up-regulated and down-regulated genes
          self.graph.vs(up_regulated.indices)["diff_expressed"] = True
          self.graph.vs(up_regulated.indices)["up_regulated"] = True
          self.graph.vs(down_regulated.indices)["diff_expressed"] = True
          self.graph.vs(down_regulated.indices)["down_regulated"] = True
  
          # add disease associations
          self._add_disease_associations(disease_associations)
  
          logger.info("Number of all differentially expressed genes is: {}".
                      format(len(up_regulated) + len(down_regulated)))