HPO Annotations (HPOAs)

HPO terms do not themselves describe diseases. Instead, the HPO project provides annotations that connect diseases to phenotypic abnormalities, forming computational disease models.

Disease models using HPO

For example,
Marfan syndrome is characterised by 50+ phenotypic abnormalities, including
Aortic root aneurysm.

Each abnormality is represented by a structured HPO term, allowing algorithms to compare patient phenotypes with known disease profiles.

How HPO annotations work

Annotation model

Example disease annotations for Familial cold autoinflammatory syndrome 2.

Annotation modifiers

Annotations can include modifiers that add clinical context, such as:

Age of onset
Frequency of a feature
Clinical qualifiers

For instance, Brachydactyly (HP:0001156) is rare in Hydrolethalus syndrome (3/56 cases in a published cohort), but occurs in nearly 100% of patients across many of the other ~484 diseases annotated with this term.

These quantitative annotations allow computational tools to weight findings when performing phenotype-driven differential diagnosis.

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