What Proportion of Annotated lncRNAs Are Functional?

Estimates cluster in the range of a few percent to roughly one-fifth of annotated lncRNAs showing a detectable phenotype in a given assay — but the number moves by an order of magnitude depending on:

• • What counts as function (viability, expression change, differentiation, organismal phenotype).
• • Where it was tested (one cell line, one condition, one timepoint).
• • How the perturbation was made (CRISPRi at the promoter, deletion, knockdown).
• • Whether redundancy was addressed (single perturbations miss buffered functions).

The useful reading is not "X% are functional" but "under these conditions, this fraction showed a detectable effect".

The disparity between rows is the point: they are measuring different things with different sensitivities.

Annotation itself is uncertain. Many annotated lncRNAs:

• • lack confirmed 5′ and 3′ ends;
• • may be transcription noise from enhancer regions;
• • overlap protein-coding loci or other non-coding features;
• • are expressed below reliable detection in most cell types.

A fraction computed against an unstable denominator should be read as an order of magnitude, not a measurement.

Perturbation designs systematically miss three classes of function:

• • Redundant functions — paralogues compensate, so single perturbations show nothing.
• • Context-restricted functions — developmental windows, stress, immune activation.
• • Cis-regulatory functions — the act of transcription matters, and promoter-level perturbations may capture it differently from transcript depletion.

Each omission pushes the estimate down, which is why "only a small fraction is functional" often reflects assay design more than biology.

• • Do not cite a proportion as a prior for your candidate. The variance across studies is too large.
• • Use expression and conservation as weak filters, not as evidence of function.
• • Design for detection: sensitized assays, relevant cell states, multiple perturbation modalities.
• • Report your own nulls with detection limits, which is how the field's estimates will eventually improve.

EDITGENE builds lncRNA perturbation series across modalities and cell states, with sensitized readouts and positive controls, so that a null carries a detection limit rather than an assumption.

Tell us the candidate and the phenotype. Contact EDITGENE to request a project consultation or quote.

Estimates of the functional fraction of lncRNAs depend on annotation version, assay sensitivity, cell type, and the definition of function; no single figure is authoritative.

Absence of a phenotype in one assay does not establish dispensability, and presence of expression or conservation does not establish function.

• • Liu SJ, et al. CRISPRi-based genome-scale identification of functional long noncoding RNA loci in human cells. Science. 2017;355:eaah7111.
• • Ramilowski JA, et al. Functional conservation of lncRNA is reflected in predicted structures and interactions. Nature Communications. 2020;11:6352.
• • Statello L, et al. Gene regulation by long non-coding RNAs and its biological functions. Nature Reviews Molecular Cell Biology. 2021;22:96–118.
• • Mattick JS, et al. Long non-coding RNAs: definitions, functions, challenges and recommendations. Nature Reviews Molecular Cell Biology. 2023;24:430–447.