BioMart does not return a result

Question

I am supplying to BioMart 81 ensemblIDs, but getting 80 results where 1 ensembleID: ENSMUSG00000083840 is absent. What does it mean if BioMart can not find the gene? Does it mean that it is a non-coding one or that there is just no symbol attached to it? Here is my BioMart query:

library('biomaRt')
mart <- useDataset("mmusculus_gene_ensembl", useMart("ensembl"))
genes <- rownames(mat)
G_list <- getBM(filters= "ensembl_gene_id", attributes= 
c("ensembl_gene_id","mgi_symbol","description"),values=genes,mart= mart)

Answer 1

Whenever you are wondering about things like this, just look up the identifier on the Ensembl web page. If you look up ENSMUSG00000083840, you will see:

This identifier is not in the current EnsEMBL database

In this case, it doesn't seem to have been replaced by anything and it wasn't a protein coding gene, so it looks like it was simply a wrong annotation which has been removed.