Hi everyone, I want to ask for ways I could do to convert mRNA ID into the gene ID. I'm using biomaRt package in R, and it works for most of the mRNA but not all of them:

ensembl <- useEnsembl(biomart = "genes", dataset = "hsapiens_gene_ensembl")
getBM(
     attributes = c("refseq_mrna", "ensembl_transcript_id", "external_gene_name"),
     filters = "refseq_mrna",
     values = "NM_000347" (for example),
     mart = ensembl
)

Yet, some of the mRNA transcripts can't be looked up this way. I want to ask how do I query those without refseq_mrna data? Thank you sm.