DNA sequencing identifies changes in the genetic sequence. RNA sequencing can show consequences of those changes, including abnormal transcript splicing, altered expression or unequal expression of two alleles. This additional layer is especially valuable when a plausible DNA finding lacks enough evidence for a confident interpretation.

Illustrated overview of from dna to rna evidence, highlighting expression, splicing, tissue relevance.
From DNA to RNA evidence: expression, splicing, tissue relevance. Read the article for evidence and limitations. Original conceptual illustration.

Choose the tissue for the question

Kremer and colleagues’ 2017 study used RNA sequencing in the investigation of suspected Mendelian disease and demonstrated how transcript-level abnormalities can help identify diagnoses. Its design also highlights a central limitation: the assay can only examine transcripts that are sufficiently represented in the tested material. A convenient sample may not reproduce the biology of an affected organ. Read the RNA-based diagnosis study.

Before interpreting a negative result, ask whether the relevant gene and transcript were expressed, whether sequencing depth was adequate, and whether an abnormal transcript might be unstable. A negative blood RNA result should not automatically exclude an effect that occurs mainly in muscle, brain or another tissue.

Use RNA as part of an evidence chain

Cummings and colleagues demonstrated the diagnostic value of transcriptome sequencing in a selected cohort with muscle disorders, including cryptic splicing abnormalities missed by earlier approaches. The work shows the strength of studying disease-relevant tissue and comparing findings with suitable reference samples. Its yield should not be generalized to every disorder or specimen type. Read the muscle transcriptome study.

An unusual RNA pattern is not automatically caused by the candidate DNA variant or responsible for the phenotype. Interpretation needs a coherent connection among the sequence change, the observed transcript effect and the established disease mechanism. Technical artifacts, normal alternative splicing and differences in cell composition can complicate that chain.

What a useful report should establish

  • The sample type and the transcripts that could be assessed reliably.
  • The abnormality observed and the comparator used to identify it.
  • The relationship between the RNA result and the candidate DNA finding.
  • The residual limitations and any need for independent confirmation.

RNA analysis can turn a speculative mechanism into measurable evidence, or reveal a mechanism that was not initially suspected. It is most useful when the clinical and laboratory teams agree beforehand on the question the assay should answer. Treat the result as a functional observation whose evidential strength depends on validation and context, rather than as an automatic diagnostic verdict.