nTPM
Also known as: normalized TPM, normalized Transcripts Per Million, TPM
Normalized Transcripts Per Million — an RNA expression unit used by the Human Protein Atlas. Reflects how many transcripts of a gene are present per million total transcripts in a sample.
Source: Human Protein Atlas (proteinatlas.org); RNA-seq methodology
nTPM (normalized Transcripts Per Million) is the RNA expression unit used throughout the Human Protein Atlas for comparing gene expression across tissues and cell types.
TPM vs. nTPM
TPM (Transcripts Per Million) is a standard RNA-seq normalization that accounts for gene length and sequencing depth, making values comparable across samples. It answers: “Of every million RNA molecules in this sample, how many came from this gene?”
nTPM is HPA’s further normalization of TPM values — aggregated and normalized across multiple samples per tissue to produce a single representative value per gene per tissue.
Practical Thresholds (HPA)
| nTPM | Interpretation |
|---|---|
| < 1 | Not detected / very low |
| 1–10 | Low expression |
| 10–100 | Medium expression |
| > 100 | High expression |
| > 1,000 | Very high expression |
HPA uses nTPM ≥ 1 as the minimum detection threshold for calling a gene “expressed” in a tissue.
Notes
- nTPM is a transcript-level measure — it does not directly reflect protein abundance (translation efficiency and protein stability vary)
- Very high nTPM (e.g., ALB in liver: >100,000 nTPM) indicates dominant, constitutive expression
- For biomarker discovery, nTPM should be read alongside tau score and fold enrichment, not in isolation