Hereditary factor IX deficiency disease

Hereditary factor IX deficiency disease is a hematologic genetic disease caused by X-linked recessive variants in F9, acting through haploinsufficiency. Within this volume's rankable burden cohort it sits at residual rank 20 of 23, where established therapy is substantially disease-modifying. That order is a provisional [H]-grade prioritisation device, not a registry-locked ranking.

Hereditary factor IX deficiency disease is inherited as X-linked recessive and acts by haploinsufficiency ([L]). Its pre-treatment burden proxy is 0.6500 and, after the established therapy's efficacy offset e = 0.5500 is applied, its residual burden score is 0.2925 ([H]), placing it at residual rank 20 of 23.

Gene, inheritance, and molecular mechanism

Hereditary factor IX deficiency disease is inherited as X-linked recessive inheritance [L] and is classified mechanistically as haploinsufficiency [L]. F9 encodes coagulation factor IX. Deficient factor IX activity impairs the intrinsic coagulation cascade, so thrombin generation is reduced.

Inheritance source: medgen:esummary:ModeOfInheritance:2026-06-17. Mechanism source: clingen:HI_score_3:2026-06-17; genes=F9; PMID:20301668,29296726. These are observed, cited inputs; the inheritance and mechanism classification is the reproducible analysis layer (C-D1).

In-scope clinical involvement

This X-linked bleeding disorder causes haemarthroses, deep-tissue bleeds, and prolonged bleeding after trauma, dental work, or surgery, graded by the residual factor IX level.

Organ systems [L] from HPO phenotype.hpoa v2026-06-06 (OMIM 306900); P-aspect terms rolled up to HP:0000118 organ-system categories via hp.obo.

Reproducible burden position

Of the five axes, 3 are scored (the rankability cut is ≥ 3 of 5); the pre-treatment composite is the renormalised mean over the scored axes, raw_burden = 0.6500. The registry-grade [L] axis here is disability (disability from the GBD 2013 disability-weights table). Onset and severity remain an [H] inference from the cited clinical definition.

Because those axes carry [H] inferences, this position is a provisional [H] prioritisation device, not a registry-locked ranking.

The natural-history registry passes have been run against Orphanet/Orphadata (CC BY 4.0, R6) and the openly published GBD 2013 disability-weights table (Salomon et al., CC BY, R7). R6 lifts onset to registry-grade [L] across most of the cohort (earliest AverageAgeOfOnset category, entity-anchored per ORPHAcode, Exact OMIM↔ORPHA only); R7 lifts disability to [L] where one dominant untreated sequela maps to a named GBD health state (published disability weight binned by declared cut-points), and independently corroborates a mortality axis from PMC survival literature where a quantitative disease-typical figure exists. Severity now lifts to registry [L] for the one disease whose dominant sequela carries a cited HPO Severity-modifier annotation (the HP:0012824 subtree, R8); for the rest the open HPO severity annotations are feature-level (using one feature as the disease tier would be a category error), so severity stays [H]/[O] with the obstacle named. Progression lifts to registry [L] where a cited PMC open-access source states a disease-level magnitude for the dominant untreated sequela and the frozen R3 tier function derives the tier from that verbatim sentence (R9, curated dominant-sequela join, non-spectrum); for the rest progression stays [H]/[O]. The OMIM clinical synopsis (the disease-level alternative) is API-key-gated and the key is unobtainable for an individual researcher — that path is removed, not guessed.

Established treatment and residual burden

The established disease-directed approach is factor IX replacement or gene therapy (etranacogene dezaparvovec). Mechanistically: restores factor IX coagulant activity; AAV gene therapy provides endogenous factor IX [L].

Its effect on natural history is classified disease-modifying (substantial), mapping to an efficacy offset e = 0.5500 and a residual factor R_treat = 0.4500. Applied to the pre-treatment proxy this gives the residual burden score 0.2925, moving the disease from raw rank 16 to residual rank 20 (shift -4).

Evidence tier: accession-dated to the GeneReviews NBK1495 Management section [L] (initial posting October 2, 2000; last revision August 7, 2025; retrieved 2026-06-18; corroborating term(s): “factor, gene”). The natural-history axis grades remain a mix of [L] (GeneReviews-corroborated) and [H] (definition-only), so the burden order is still provisional.