The following genes with an identifier have been found but that do not have a mapping to Ensembl: 3
http://classic.wikipathways.org/instance/WP222_r116835 H2-Ea with datasource Entrez Gene
http://classic.wikipathways.org/instance/WP222_r116835 TRB with datasource Entrez Gene
http://classic.wikipathways.org/instance/WP222_r116835 Tcra with datasource MGI
More details at https://www.wikipathways.org/WikiPathwaysCurator/GeneTests/genesWithoutEnsemblMapping