LARGELY UNKNOWN. “Besides these classical ncRNAs, there are various ncRNAs of unknown function, many of which are considered as lncRNAs based on their size greater being than 200 nucleotides. These, apart from the lack of protein-coding potential, have relatively low levels of evolutionary conservation and originate from genes that are usually shorter than protein-coding genes, with fewer exons.” (ncRNAs = non-protein coding RNAs; IncRNAs = antisense long non-coding RNAs).
http://www.mdpi.com/1422-0067/16/2/3251/htm