hpo-drift

What did a new HPO release change for your phenotype terms — and by how much did your similarity scores move?

The Human Phenotype Ontology is updated regularly. Terms get renamed, obsoleted and merged — and, the part nobody notices, the hierarchy gets new edges. New edges change information content, and information content is what Resnik and Lin similarity are made of. So the same patient set, scored against two HPO releases, gives different numbers even if none of your terms were touched. hpo-drift shows you exactly that, for the term list you actually use, in about three seconds.

The headline result

Feb 2026 → Jun 2026. The example is the HPO-annotated phenotype profile of familial isolated hypoparathyroidism (OMIM:146200): 11 phenotypic-abnormality terms straight from phenotype.hpoa. I chose it because the mechanism is a single edit that any clinician can judge. Then, as a sanity check, hpo-drift cohort ran over the complete phenotype.hpoa corpus — 12 935 disease profiles, no size cutoff: 11 947 have at least one informative pair, 705 are single-term, 283 have root-only pairs, all of them stay in the table with a status — and hpo-drift rank ordered the rankable ones by mean |ΔLin|. This profile is 20th of 11 947 (median profile 0.0013, 99th percentile 0.043); the same edit drives four of the top five (isolated hypoparathyroidism ×2, parathyroid agenesis, pseudohypoparathyroidism type 2).

What happened to this profile, computed with Seco intrinsic IC on the is_a graph under Phenotypic abnormality:

• One term lost one parent. Hypocalcemic seizures (HP:0002199) was is_a Hypocalcemia (HP:0002901) and is_a Symptomatic seizures; in v2026-06-23 the Hypocalcemia edge is gone (so is the same edge under Hypocalcemic tetany, HP:0003472). No label changed, nothing was obsoleted, the other 10 terms were not touched.
• Consequence: Hypocalcemic seizures ↔ Hypocalcemia went 0.94 → 0.00 — their most-informative common ancestor is now the root. Hypocalcemic seizures ↔ Hyperphosphatemia 0.59 → 0.00, ↔ Decreased circulating PTH level 0.21 → 0.00. Hypocalcemia itself, having lost its last child, became a leaf: IC 0.888 → 1.000, which nudges its pairs with Hyperphosphatemia (0.63 → 0.59) and PTH level.
• 14 informative pairs, all 14 moved, 3 of them by more than 0.1; 41 pairs share only the root (ROOT_ONLY, 0 → 0). IC moved by more than 0.01 for 1 of 11 terms. Mean |ΔLin| 0.129; the median disease profile: 0.0013.

Whether the edit is right is an ontology-design question (a seizure caused by hypocalcemia is arguably not a kind of hypocalcemia). What is not a matter of opinion: a phenotype-similarity score between two terms that share half their name went from near-identical to zero, without changing the input phenotype profile. Pin the release tag in Methods, match on IDs, and report how much the numbers depend on the release. hpo-drift gives you that sentence with real figures; hpo-drift cohort tells you where your disease of interest sits.

Reproduce (the annotation file is pinned: phenotype.hpoa from HPO release v2026-06-23, #version: 2026-06-23, SHA-256 89004f85b253f980ffe84218d2c080665cbf67a57bbb322111d6a2db5eb31dff; the script prints the version and hash of the file it was given):

curl -LO https://github.com/obophenotype/human-phenotype-ontology/releases/download/v2026-06-23/phenotype.hpoa
hpo-drift cohort --hpoa phenotype.hpoa --old v2026-02-16 --new v2026-06-23 --out all_profiles.csv   # every profile, ~30 s
hpo-drift rank all_profiles.csv --metric mean_abs_dlin > ranked.csv                                  # optional

Output as run on 2026-09-03: examples/cohort-v2026-02-16_v2026-06-23.csv (all 12 935 profiles with status, plus a .meta.json recording the annotation file's version and hash) and examples/ranked-v2026-02-16_v2026-06-23.csv. Where familiar syndromes sit: X-linked agammaglobulinemia 0.033, autosomal dominant hyper-IgE syndrome 0.029, cystic fibrosis 0.023, Wiskott–Aldrich 0.020, Kabuki / Noonan / Marfan about 0.001.

30-second start

pip install hpo-drift

# one term per line — HP IDs (recommended) or labels
hpo-drift report --old v2026-02-16 --new v2026-06-23 --terms examples/fih_omim146200_terms.txt

IC: Seco 2004 intrinsic, on the is_a graph under root HP:0000118 (Phenotypic abnormality); N = 18690 → 19120
active terms: 19389 → 19836 (added 469, obsoleted 22, renamed 266)
is_a edges:   +886 / −185

term        label                  status     parents        IC old → new
HP:0002199  Hypocalcemic seizures  unchanged  −HP:0002901    1.000 → 1.000
HP:0002901  Hypocalcemia           unchanged  =              0.888 → 1.000
…
pair                                      Lin old → new   Δ       MICA
Hypocalcemic seizures ↔ Hypocalcemia      0.941 → 0.000   −0.941  HP:0002901 → HP:0000118
Hypocalcemic seizures ↔ Hyperphosphatemia 0.594 → 0.000   −0.594  HP:0003111 → HP:0000118
…

Add --json for a machine-readable report. Releases are pulled from the official GitHub assets of obophenotype/human-phenotype-ontology; any tag like v2026-06-23 works and is cached under ~/.cache/hpo-drift.

Four things it does

1 · report — the drift itself

Per term: status (unchanged / renamed / obsoleted → replacement / merged / missing), label change, parents added or removed, IC before and after. Per pair: Resnik and Lin in both releases, the delta, and the most-informative common ancestor — so you can see why a pair moved. Plus the ontology-wide counts.

2 · lint — hygiene for a term list

hpo-drift lint --release v2026-06-23 --terms my_terms.txt

⚠️ Arthritis: matched by LABEL — labels get renamed; store the ID → HP:0001369
❌ Recurrent infection: label not found (exact match on names/synonyms; the term is 'Recurrent infections')
❌ HP:0002961: OBSOLETE term → replaced_by HP:0010701

Exit code 1 on errors, so it works as a CI gate for a phenotype spreadsheet. Matching is exact on purpose: it reproduces the failure mode of a pipeline that matches by label. Store IDs, not labels: 266 labels changed in this interval alone, and fuzzy resolution (roadmap) must suggest, never auto-map.

3 · cohort and rank — the whole annotation corpus, no cutoffs

hpo-drift cohort --hpoa phenotype.hpoa --old v2026-02-16 --new v2026-06-23 --out all_profiles.csv
hpo-drift rank all_profiles.csv --metric mean_abs_dlin --top 20

cohort computes the drift summary for every disease with at least one positive phenotypic-abnormality annotation in phenotype.hpoa — a profile is the unique HP ids of a disease's rows with aspect P and no NOT qualifier (in v2026-06-23: 12 956 disease ids in the file, 12 935 profiles, 21 ids have only negated or non-P rows; the sidecar .meta.json records both counts). There is no minimum or maximum size: a profile that cannot support pairwise analysis stays in the table with a status — NO_USABLE_TERMS, TERM_ONLY (IC drift only), NO_INFORMATIVE_PAIRS (every pair shares only the root) or RANKABLE. Columns: a mutually exclusive disposition of every raw term (retained, unknown, new_only, missing_new, merged_or_alt, obsolete, out_of_domain — they add up to n_raw_terms), IC changes, pairs split into informative and root-only, pairs changed and pairs moved by > 0.01 / > 0.1, mean and max |ΔLin|. rank is a separate, optional step over that complete table. report follows the same rules for any list you give it: 0, 1 or N terms, root-only pairs marked ROOT_ONLY, terms outside the root marked OUT_OF_DOMAIN with a pointer to --root. IDs and labels are resolved against both releases: a term that exists only in the new release is reported as new-in-new (not silently dropped), a label the two releases map to different ids as ambiguous, an unresolvable token as unknown.

Provenance. Every hp.obo is downloaded atomically, hashed, checked against the SHA-256 the official HPO GitHub release publishes for the asset, and cached only after that check; reports, JSON and cohort sidecars record the SHA-256 of both ontology inputs and of the annotation file.

4 · a monthly GitHub Action

.github/workflows/drift.yml fetches the latest release, compares it with your pinned one (PINNED_HPO) and uploads the report. Add a threshold on lin_delta from the JSON and it becomes a failing check.

How it works

flowchart LR
  A["release tag<br/>v2026-02-16"] -->|hp.obo| C[parse: terms · is_a · alt_id · obsolete]
  B["release tag<br/>v2026-06-23"] -->|hp.obo| C
  C --> D["intrinsic IC<br/>Seco 2004"]
  T[your term list] --> E[resolve IDs / labels]
  E --> F[per-term status · parents · IC Δ]
  D --> G[Resnik / Lin per pair · MICA · Δ]
  F --> R[report · JSON · lint]
  G --> R

IC is intrinsic (Seco et al. 2004: 1 − log(descendants+1)/log(N)), computed on the is_a graph only, with N and descendant counts taken inside the closure of a root — HP:0000118 Phenotypic abnormality by default (--root to change; inheritance, frequency and modifier branches are excluded, and the root's IC is exactly 0). Every report states the method, the root and N. Because this IC depends only on the graph, the drift measured here is caused purely by ontology edits, which is the effect this tool isolates. Annotation-based IC (from phenotype.hpoa) adds a second, independent source of drift and is the next option on the roadmap — then the two can be shown side by side.

Companion tools

• hpotools — HPO in R: release-pinned loading, similarity, Phenomizer-style ranking, enrichment.
• awesome-human-phenotype-ontology — link-verified list of HPO tools.

Roadmap

--ic annotations · fuzzy label suggestions in lint · Phenopackets v2 export · --pairs file for patient × disease scoring · JOSS paper.

Cite

DOI (all versions): 10.5281/zenodo.22286170 — each release has its own version DOI on that Zenodo page; cite the version you ran (hpo-drift --version).

Soloshenko M. hpo-drift: quantifying the effect of HPO release changes on phenotype-similarity results. 2026. MIT License.