I have a list of gene symbol and obtaine the corresponding Ensembl gene ID for some of them via Biomart; But, it was unavailable for many genes;however, I can find the related Ensembl gene ID for these genes, one-by-one, at GeneCards. It's really time-consuming as GeneCards doesn't accept the gene list. Could you please let me know your solution at this situation?
Also, in some cases, there are various Ensembl gene IDs for the same gene symbol; say, AATF, Biomart reported ENSG00000275700 and ENSG00000276072 for this gene, which just ENSG00000275700 is available at GeneCards. There is also similar issue with more than 2 or even 5 Ensembl ID for them. Please kindly tell me what is the story here?