Thanatophoric dysplasia (TD) is the commonest neonatal-lethal skeletal dysplasia, caused by de novo heterozygous gain-of-function variants in FGFR3. It is a short-limb chondrodysplasia with micromelia, short ribs and a narrow thorax, relative macrocephaly, brachydactyly, hypotonia, redundant skin folds and distinctive facial features; most affected infants die of respiratory insufficiency shortly after birth, with rare long-term survivors on intensive respiratory support. TD is divided into two subtypes distinguished by femur and skull shape and by the underlying FGFR3 allele: TD type 1 (curved/bowed femurs, craniosynostosis uncommon; heterogeneous alleles including R248C, Y373C, S249C, S371C and the stop-codon-extension changes) and TD type 2 (straight femurs with uniform moderate-to-severe craniosynostosis and cloverleaf skull; essentially always the K650E kinase-domain change). This root entry deliberately carries only what is reported for TD as a whole — the TD-level birth prevalence, the shared prenatal-ultrasound to radiographic to molecular-confirmation diagnostic pathway (one assay covers both subtypes), the allelic-series framing that places TD at the severe end of the FGFR3 gradient, the TD1/TD2 discriminator, and the thoracic-insufficiency step that makes the disorder lethal. The receptor biology and the growth-plate cascade are not re-derived here; they are held once in the `fgfr_gain_of_function_skeletal_dysplasia` module, and the full subtype detail lives in the Thanatophoric Dysplasia Type 1 and Type 2 entries.
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Conditions with similar clinical presentations that must be differentiated from Thanatophoric Dysplasia:
name: Thanatophoric Dysplasia
creation_date: '2026-08-19T00:00:00Z'
category: Mendelian
description: >
Thanatophoric dysplasia (TD) is the commonest neonatal-lethal skeletal dysplasia,
caused by de novo heterozygous gain-of-function variants in FGFR3. It is a short-limb
chondrodysplasia with micromelia, short ribs and a narrow thorax, relative macrocephaly,
brachydactyly, hypotonia, redundant skin folds and distinctive facial features; most
affected infants die of respiratory insufficiency shortly after birth, with rare
long-term survivors on intensive respiratory support. TD is divided into two subtypes
distinguished by femur and skull shape and by the underlying FGFR3 allele: TD type 1
(curved/bowed femurs, craniosynostosis uncommon; heterogeneous alleles including
R248C, Y373C, S249C, S371C and the stop-codon-extension changes) and TD type 2
(straight femurs with uniform moderate-to-severe craniosynostosis and cloverleaf
skull; essentially always the K650E kinase-domain change).
This root entry deliberately carries only what is reported for TD as a whole — the
TD-level birth prevalence, the shared prenatal-ultrasound to radiographic to
molecular-confirmation diagnostic pathway (one assay covers both subtypes), the
allelic-series framing that places TD at the severe end of the FGFR3 gradient, the
TD1/TD2 discriminator, and the thoracic-insufficiency step that makes the disorder
lethal. The receptor biology and the growth-plate cascade are not re-derived here;
they are held once in the `fgfr_gain_of_function_skeletal_dysplasia` module, and the
full subtype detail lives in the Thanatophoric Dysplasia Type 1 and Type 2 entries.
disease_term:
preferred_term: thanatophoric dysplasia
term:
id: MONDO:0017042
label: thanatophoric dysplasia
synonyms:
- TD
- thanatophoric dwarfism
- FGFR3-related thanatophoric dysplasia
parents:
- FGFR3-related chondrodysplasia
- Lethal skeletal dysplasia
- Osteochondrodysplasia
classifications:
isds_skeletal_category:
- classification_value: fgfr3_chondrodysplasia
notes: >-
ISDS Nosology and Classification of Genetic Skeletal Disorders, 2019 revision
(Mortier et al., PMID:31633310), Table 1 group 1 "FGFR3 chondrodysplasia group",
which lists thanatophoric dysplasia types 1 and 2 alongside achondroplasia,
hypochondroplasia and SADDAN. MONDO places the same concept under
MONDO:0019685 FGFR3-related chondrodysplasia.
inheritance:
- name: Autosomal dominant (de novo)
description: >-
TD is transmitted as an autosomal dominant trait, but because it is a perinatally
lethal condition affected individuals do not reproduce, so essentially every
proband carries a de novo FGFR3 variant. Sib recurrence risk is not appreciably
raised above the population rate; germline mosaicism in a healthy parent remains
a theoretical possibility that has not been reported.
inheritance_term:
preferred_term: Autosomal dominant inheritance
term:
id: HP:0000006
label: Autosomal dominant inheritance
evidence:
- reference: PMID:20301540
reference_title: Thanatophoric Dysplasia.
supports: SUPPORT
evidence_source: OTHER
snippet: >-
TD is inherited in an autosomal dominant manner; the majority of probands have a de novo FGFR3 pathogenic variant.
explanation: >-
GeneReviews states the mode of inheritance and the predominance of de novo
variants for thanatophoric dysplasia as a whole.
- reference: PMID:20301540
reference_title: Thanatophoric Dysplasia.
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Germline mosaicism in healthy parents, although not reported to date, remains a theoretic possibility.
explanation: >-
Bounds the recurrence mechanism: germline mosaicism is unreported rather than
established, so it is recorded as a theoretical possibility only.
- reference: PMID:42547059
reference_title: >-
Thanatophoric dysplasia: prevalence, clinical characteristics, and molecular
findings in a public hospital from Western Mexico.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
All presented TD1 (4 men and 6 women), sporadic occurrence and 4/10 advanced paternal age.
explanation: >-
A consecutive hospital birth series in which every ascertained TD case was
sporadic, consistent with de novo occurrence; the advanced-paternal-age skew is
the expected signature of a paternally-derived de novo point mutation.
has_subtypes:
- name: TD1
display_name: Thanatophoric dysplasia type 1
classification: clinical
description: >-
Micromelia with curved (bowed, "telephone receiver") femurs; craniosynostosis is
present only uncommonly and cloverleaf skull is unusual. Caused by a heterogeneous
set of FGFR3 alleles, most often the extracellular/juxtamembrane cysteine-creating
changes R248C, Y373C, S249C, S371C and G370C, plus the stop-codon-extension
changes in exon 18. Curated in full in `Thanatophoric_Dysplasia_Type_1.yaml`.
subtype_term:
preferred_term: thanatophoric dysplasia type 1
term:
id: MONDO:0008546
label: thanatophoric dysplasia type 1
genes:
- preferred_term: FGFR3
term:
id: hgnc:3690
label: FGFR3
evidence:
- reference: PMID:20301540
reference_title: Thanatophoric Dysplasia.
supports: SUPPORT
evidence_source: OTHER
snippet: >-
TD type 1 is characterized by micromelia with bowed femurs and, uncommonly, the presence of craniosynostosis of varying severity.
explanation: >-
GeneReviews defines the TD1 subtype by bowed femurs and the low frequency of
craniosynostosis.
- reference: PMID:42547059
reference_title: >-
Thanatophoric dysplasia: prevalence, clinical characteristics, and molecular
findings in a public hospital from Western Mexico.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
In seven, pathogenic variants in FGFR3 were identified: p.Arg248Cys (n = 3), p.Ser371Cys (n = 2), p.Gly370Cys (n = 1) and p.Try373Cys (n = 1).
explanation: >-
Documents the allelic heterogeneity of TD1 in a consecutive series — four
different FGFR3 changes across seven molecularly solved cases — in contrast to
the essentially invariant TD2 allele.
- name: TD2
display_name: Thanatophoric dysplasia type 2
classification: clinical
description: >-
Micromelia with straight femurs and uniform moderate-to-severe craniosynostosis
with cloverleaf skull deformity. Essentially always caused by the single recurrent
FGFR3 p.Lys650Glu (K650E) change in the tyrosine kinase domain. Curated in full in
`Thanatophoric_Dysplasia_Type_2.yaml`.
subtype_term:
preferred_term: thanatophoric dysplasia type 2
term:
id: MONDO:0008547
label: thanatophoric dysplasia type 2
genes:
- preferred_term: FGFR3
term:
id: hgnc:3690
label: FGFR3
evidence:
- reference: PMID:20301540
reference_title: Thanatophoric Dysplasia.
supports: SUPPORT
evidence_source: OTHER
snippet: >-
TD type 2 is characterized by micromelia with straight femurs and uniform presence of moderate-to-severe craniosynostosis with cloverleaf skull deformity.
explanation: >-
GeneReviews defines the TD2 subtype by straight femurs and the constant presence
of cloverleaf skull, the two features that separate it from TD1 radiologically.
- reference: PMID:7773297
reference_title: >-
Thanatophoric dysplasia (types I and II) caused by distinct mutations in
fibroblast growth factor receptor 3.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
A sporadic mutation causing a Lys650Glu change in the tyrosine kinase domain
of FGFR3 was found in 16 of 16 individuals with one type of TD.
explanation: >-
The original demonstration that a single kinase-domain allele accounts for the
TD2 subtype in every case examined — the molecular half of the TD1/TD2
discriminator.
prevalence:
- population: Worldwide (live births)
measure_type: BIRTH_PREVALENCE
prevalence_class: BAND_1_9_PER_100000
rate_per_100000: 5.0
notes: >-
Long-standing 1 in 20,000 live-birth figure from the original FGFR3 mutation
series; predates routine prenatal ascertainment and termination, so it is not
directly comparable with the surveillance estimates below.
evidence:
- reference: PMID:7773297
reference_title: >-
Thanatophoric dysplasia (types I and II) caused by distinct mutations in
fibroblast growth factor receptor 3.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Thanatophoric dysplasia (TD), the most common neonatal lethal skeletal
dysplasia, affects one out of 20,000 live births.
explanation: >-
States the live-birth frequency of thanatophoric dysplasia as a whole, and its
standing as the commonest neonatal-lethal skeletal dysplasia.
- population: United States, four population-based birth-defects surveillance programs (Atlanta, Iowa, Oklahoma, Texas)
measure_type: BIRTH_PREVALENCE
prevalence_class: BAND_1_9_PER_100000
rate_low: 2.1
rate_high: 3.0
notes: >-
0.21-0.30 per 10,000 livebirths (1 in 47,620 to 1 in 33,330), reported for
thanatophoric dysplasia overall rather than by subtype. Registries ascertained
livebirths, late fetal deaths and elective terminations, so the estimate is less
depressed by prenatal termination than a livebirth-only count would be.
evidence:
- reference: PMID:18698630
reference_title: >-
The population-based prevalence of achondroplasia and thanatophoric dysplasia
in selected regions of the US.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
The prevalence of thanatophoric dysplasia ranged from 0.21 to 0.30 per 10,000
livebirths (1/33,330-1/47,620 livebirths).
explanation: >-
Population-based US birth prevalence for thanatophoric dysplasia as a single
entity across four surveillance programs.
- reference: PMID:18698630
reference_title: >-
The population-based prevalence of achondroplasia and thanatophoric dysplasia
in selected regions of the US.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
These data suggest that thanatophoric dysplasia is one-third to one-half as
frequent as achondroplasia.
explanation: >-
Anchors TD's occurrence against achondroplasia, the reference point of the same
FGFR3 allelic series, within a single ascertainment framework.
- population: Western Mexico, Hospital Civil de Guadalajara Dr. Juan I. Menchaca, 2009-2024
measure_type: BIRTH_PREVALENCE
prevalence_class: BAND_1_9_PER_100000
rate_per_100000: 8.5
rate_low: 3.2
rate_high: 13.7
notes: >-
0.85 per 10,000 births (95% CI 0.32-1.37); 10 TD births in 118,154, i.e. 1 in
11,815. Single-hospital referral series, materially higher than the US
surveillance figure; all ten cases were TD1.
evidence:
- reference: PMID:42547059
reference_title: >-
Thanatophoric dysplasia: prevalence, clinical characteristics, and molecular
findings in a public hospital from Western Mexico.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
The prevalence of TD was 0.85 per 10,000 births (95% CI: 0.32-1.37).
explanation: >-
A second, independent population estimate of TD birth prevalence, reported for
TD as a whole with a confidence interval.
- reference: PMID:42547059
reference_title: >-
Thanatophoric dysplasia: prevalence, clinical characteristics, and molecular
findings in a public hospital from Western Mexico.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Ten live births with TD were included from a total of 118,154 births between 2009 and 2024 at the Hospital Civil de Guadalajara Dr. Juan I. Menchaca (Mexico).
explanation: >-
Gives the numerator and denominator behind the rate. Recorded as PARTIAL because
a single tertiary referral hospital is not a defined source population, so the
point estimate is not directly comparable with the population-based US figure.
progression:
- phase: Perinatal death from respiratory insufficiency
age_range: Birth to the first days of life
notes: >-
Death in the perinatal period is the expected outcome. This is curated under
`progression` rather than as a `phenotypes` entry because the corresponding HPO
terms (HP:0003811 Neonatal death, HP:0001522 Death in infancy) sit in the HPO
clinical-modifier/mortality branch rather than under HP:0000118 Phenotypic
abnormality, and so are not members of the PhenotypeTerm dynamic enum — the same
convention already used in `Cardiomyopathy-Hypotonia-Lactic_Acidosis_Syndrome.yaml`
and `Arthrogryposis-Renal_Dysfunction-Cholestasis_Syndrome.yaml`.
evidence:
- reference: PMID:20301540
reference_title: Thanatophoric Dysplasia.
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Most affected infants die of respiratory insufficiency shortly after birth. Rare long-term survivors have been reported.
explanation: >-
GeneReviews states the timing and mode of death for TD as a whole, and that
long-term survival is exceptional.
- reference: PMID:18698630
reference_title: >-
The population-based prevalence of achondroplasia and thanatophoric dysplasia
in selected regions of the US.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Of the 29 cases that were born alive, medical records indicated that 28 died during the neonatal period.
explanation: >-
Quantifies neonatal lethality in a population-based surveillance series, 28 of 29
liveborn cases, rather than relying on a narrative term.
pathophysiology:
- name: Graded FGFR3 Gain-of-Function Activation
conforms_to: "fgfr_gain_of_function_skeletal_dysplasia#Constitutive FGFR Activation"
biological_scale: MOLECULAR
role: trigger
description: >-
Every TD allele constitutively activates FGFR3 — ligand-independent receptor
tyrosine phosphorylation and ligand-independent proliferative signalling — but the
defining feature at the root level is that the TD alleles activate the receptor
more strongly than the achondroplasia G380R allele does. This graded activation is
the mechanistic basis of the FGFR3 severity gradient: hypochondroplasia (N540K),
achondroplasia (G380R), SADDAN (K650M), thanatophoric dysplasia (R248C and related
extracellular cysteine changes; K650E). Homozygous achondroplasia, which doubles
the dose of a weaker allele, phenocopies TD — the dose-response corollary of the
same claim. The receptor biology itself is held once in the
`fgfr_gain_of_function_skeletal_dysplasia` module and is not re-derived here; see
`Achondroplasia.yaml`, `Hypochondroplasia.yaml`, `SADDAN.yaml` and
`Crouzon_Syndrome_with_Acanthosis_Nigricans.yaml` for the other points on the
gradient.
genes:
- preferred_term: FGFR3
term:
id: hgnc:3690
label: FGFR3
modifier: GAIN_OF_FUNCTION
molecular_functions:
- preferred_term: transmembrane receptor protein tyrosine kinase activity
term:
id: GO:0004714
label: transmembrane receptor protein tyrosine kinase activity
modifier: INCREASED
biological_processes:
- preferred_term: fibroblast growth factor receptor signaling pathway
term:
id: GO:0008543
label: fibroblast growth factor receptor signaling pathway
modifier: INCREASED
evidence:
- reference: PMID:8640234
reference_title: >-
Graded activation of fibroblast growth factor receptor 3 by mutations causing
achondroplasia and thanatophoric dysplasia.
supports: SUPPORT
evidence_source: IN_VITRO
snippet: >-
Moreover, the mutations that are responsible for TD were more strongly
activating than the mutation causing ACH, providing a biochemical explanation
for the observation that the phenotype of TD is more severe than that of ACH.
explanation: >-
The direct biochemical anchor for the allelic-series claim: TD alleles are more
strongly activating than the achondroplasia allele, which is why TD sits at the
lethal end of the same FGFR3 gradient.
- reference: PMID:8640234
reference_title: >-
Graded activation of fibroblast growth factor receptor 3 by mutations causing
achondroplasia and thanatophoric dysplasia.
supports: SUPPORT
evidence_source: IN_VITRO
snippet: >-
We showed that each of the mutations constitutively activate the receptor, as
evidenced by ligand-independent receptor tyrosine phosphorylation and cell
proliferation.
explanation: >-
Establishes that the shared direction of effect across the series is
constitutive, ligand-independent receptor activation — the module's trigger node.
- reference: PMID:8640234
reference_title: >-
Graded activation of fibroblast growth factor receptor 3 by mutations causing
achondroplasia and thanatophoric dysplasia.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Homozygous achondroplasia resembles the phenotype of TD.
explanation: >-
The dose-response corollary of graded activation: doubling a weaker allele
reproduces the phenotype of a single stronger one, which is what a severity
gradient driven by receptor-activation strength predicts.
- reference: PMID:7773297
reference_title: >-
Thanatophoric dysplasia (types I and II) caused by distinct mutations in
fibroblast growth factor receptor 3.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
None of these mutations were found in 50 controls showing that mutations
affecting different functional domains of FGFR3 cause different forms of this
lethal disorder.
explanation: >-
Establishes that the TD1 and TD2 subtypes are separated by which functional
domain of FGFR3 the activating change lies in, not by a different gene or a
different direction of effect.
downstream:
- target: Severe Endochondral Growth Failure and Micromelia
description: >-
Strong constitutive FGFR3 signalling in growth-plate cartilage suppresses
longitudinal endochondral bone growth. The intermediates (sustained MAPK/ERK and
STAT1 signalling, chondrocyte proliferation arrest and impaired hypertrophic
differentiation) are curated once in the
fgfr_gain_of_function_skeletal_dysplasia module and in the TD1 and TD2 entries;
they are deliberately not duplicated at the root.
causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
- name: Severe Endochondral Growth Failure and Micromelia
conforms_to: "fgfr_gain_of_function_skeletal_dysplasia#Impaired Endochondral Ossification and Chondrodysplasia"
biological_scale: TISSUE
role: effector
description: >-
Endochondral ossification fails throughout the appendicular and axial skeleton,
producing extreme micromelia, platyspondyly and — critically — short ribs.
Histologically the growth plate shows disordered ossification with chondrocyte
hyperplasia and loss of the orderly proliferative columns. At the root level this
node exists to carry the step from cartilage failure to the thoracic dimension;
the zone-by-zone growth-plate detail belongs to the module and the subtype entries.
cell_types:
- preferred_term: Growth-plate chondrocyte
term:
id: CL:0000138
label: chondrocyte
- preferred_term: Hypertrophic chondrocyte
term:
id: CL:0000743
label: hypertrophic chondrocyte
biological_processes:
- preferred_term: endochondral ossification
term:
id: GO:0001958
label: endochondral ossification
modifier: DECREASED
- preferred_term: growth plate cartilage development
term:
id: GO:0003417
label: growth plate cartilage development
modifier: DYSREGULATED
evidence:
- reference: PMID:20301540
reference_title: Thanatophoric Dysplasia.
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Thanatophoric dysplasia (TD) is a short-limb skeletal dysplasia that is usually lethal in the perinatal period.
explanation: >-
Establishes the disorder-level readout of the endochondral failure — a short-limb
dysplasia — and its perinatal lethality, for TD as a whole rather than by subtype.
- reference: PMID:39778871
reference_title: >-
An immunohistochemical study of thanatophoric dysplasia type 1 after fetus
autopsy examination.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Microscopical evaluation indicated inadequate histological growth for the gestational age, with specific organ immaturity noted in multiple hematoxylin and eosin sections from internal organs, bone from epiphyses and diaphyses levels.
explanation: >-
Direct human fetal-autopsy histology showing growth inadequate for gestational
age at the epiphyseal and diaphyseal levels, the tissue-level correlate of
failed endochondral ossification.
downstream:
- target: Thoracic Insufficiency and Pulmonary Hypoplasia
description: >-
Short ribs and a small, bell-shaped thorax restrict the volume available for
lung growth and for chest-wall excursion after birth.
causal_link_type: DIRECT
- name: Thoracic Insufficiency and Pulmonary Hypoplasia
biological_scale: ORGANISM
role: consequence
description: >-
The step that makes thanatophoric dysplasia lethal, and the one part of the chain
that is TD-specific rather than shared with the viable members of the FGFR3
allelic series. Severely shortened ribs and a narrow thorax restrict fetal lung
growth and neonatal chest-wall excursion; respiratory insufficiency is the
immediate cause of death in the great majority of affected infants. Survival
beyond the perinatal period has been reported only with long-term tracheostomy and
ventilation. This node is deliberately not anchored on the FGFR module:
achondroplasia and hypochondroplasia share every upstream node and do not reach
this one.
locations:
- preferred_term: lung
term:
id: UBERON:0002048
label: lung
biological_processes:
- preferred_term: lung development
term:
id: GO:0030324
label: lung development
modifier: DECREASED
- preferred_term: respiratory gaseous exchange
term:
id: GO:0007585
label: respiratory gaseous exchange by respiratory system
modifier: DECREASED
evidence:
- reference: PMID:20301540
reference_title: Thanatophoric Dysplasia.
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Most affected infants die of respiratory insufficiency shortly after birth. Rare long-term survivors have been reported.
explanation: >-
GeneReviews states, for TD as a whole, that respiratory insufficiency is the
mode of perinatal death and that survival is exceptional.
- reference: PMID:20301540
reference_title: Thanatophoric Dysplasia.
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Newborns require long-term respiratory support (typically with tracheostomy and ventilation) to survive.
explanation: >-
Identifies the thoracic and respiratory limitation, rather than any other organ
failure, as the rate-limiting constraint on survival.
- reference: PMID:39778871
reference_title: >-
An immunohistochemical study of thanatophoric dysplasia type 1 after fetus
autopsy examination.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
In the lungs, pseudoglandular growth predominated, transitioning partially to an early canalicular phase, and incomplete development was noted in bronchi, with primary and a few secondary bronchi visible, covered with pseudostratified columnar ciliated epithelium, with scattered goblet cells
explanation: >-
Human fetal-autopsy evidence of lung immaturity in TD1. Recorded as PARTIAL
because at 17 weeks the pseudoglandular-to-canalicular transition is close to
the normal developmental stage, so this documents the pulmonary phenotype
without on its own demonstrating rib-cage-driven hypoplasia.
phenotypes:
- category: Skeletal
name: Micromelia
description: >-
Extreme shortening of all four limbs, present in both TD subtypes and the feature
that brings the pregnancy to attention on ultrasound.
phenotype_term:
preferred_term: Micromelia
term:
id: HP:0002983
label: Micromelia
frequency: VERY_FREQUENT
evidence:
- reference: PMID:20301540
reference_title: Thanatophoric Dysplasia.
supports: SUPPORT
evidence_source: OTHER
snippet: >-
TD type 1 is characterized by micromelia with bowed femurs and, uncommonly, the presence of craniosynostosis of varying severity. TD type 2 is
characterized by micromelia with straight femurs and uniform presence of
moderate-to-severe craniosynostosis with cloverleaf skull deformity.
explanation: >-
GeneReviews describes micromelia as definitional for both subtypes, which is why
it is curated at the root rather than per subtype.
- category: Skeletal
name: Short ribs
description: >-
Severely shortened ribs, the structural cause of the narrow thorax and hence of the
respiratory insufficiency that kills most affected infants.
phenotype_term:
preferred_term: Short ribs
term:
id: HP:0000773
label: Short ribs
frequency: VERY_FREQUENT
diagnostic: true
evidence:
- reference: PMID:20301540
reference_title: Thanatophoric Dysplasia.
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Other features common to type 1 and type 2 include: short ribs, narrow thorax, relative macrocephaly, distinctive facial features, brachydactyly, hypotonia, and redundant skin folds along the limbs.
explanation: >-
GeneReviews lists short ribs explicitly as a feature common to both TD subtypes.
- category: Skeletal
name: Narrow thorax
description: >-
A small, bell-shaped chest with reduced thoracic circumference, common to both
subtypes and the proximate cause of pulmonary hypoplasia.
phenotype_term:
preferred_term: Narrow chest
term:
id: HP:0000774
label: Narrow chest
frequency: VERY_FREQUENT
diagnostic: true
evidence:
- reference: PMID:20301540
reference_title: Thanatophoric Dysplasia.
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Other features common to type 1 and type 2 include: short ribs, narrow thorax, relative macrocephaly, distinctive facial features, brachydactyly, hypotonia, and redundant skin folds along the limbs.
explanation: >-
GeneReviews lists narrow thorax as common to both TD subtypes.
- category: Craniofacial
name: Relative macrocephaly
description: >-
Head circumference large relative to the severely shortened trunk and limbs, common
to both subtypes.
phenotype_term:
preferred_term: Macrocephaly
term:
id: HP:0000256
label: Macrocephaly
frequency: VERY_FREQUENT
evidence:
- reference: PMID:20301540
reference_title: Thanatophoric Dysplasia.
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Other features common to type 1 and type 2 include: short ribs, narrow thorax, relative macrocephaly, distinctive facial features, brachydactyly, hypotonia, and redundant skin folds along the limbs.
explanation: >-
GeneReviews lists relative macrocephaly as common to both TD subtypes.
- category: Craniofacial
name: Distinctive facial features
description: >-
A recognisable facies, shared by both subtypes. The HPO binding is deliberately the
general term because the GeneReviews abstract does not enumerate the component
features; per-feature detail is curated in the subtype entries.
phenotype_term:
preferred_term: Abnormal facial shape
term:
id: HP:0001999
label: Abnormal facial shape
frequency: VERY_FREQUENT
evidence:
- reference: PMID:20301540
reference_title: Thanatophoric Dysplasia.
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Other features common to type 1 and type 2 include: short ribs, narrow thorax, relative macrocephaly, distinctive facial features, brachydactyly, hypotonia, and redundant skin folds along the limbs.
explanation: >-
GeneReviews lists distinctive facial features as common to both TD subtypes.
- category: Skeletal
name: Brachydactyly
description: Short digits, common to both subtypes.
phenotype_term:
preferred_term: Brachydactyly
term:
id: HP:0001156
label: Brachydactyly
frequency: VERY_FREQUENT
evidence:
- reference: PMID:20301540
reference_title: Thanatophoric Dysplasia.
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Other features common to type 1 and type 2 include: short ribs, narrow thorax, relative macrocephaly, distinctive facial features, brachydactyly, hypotonia, and redundant skin folds along the limbs.
explanation: >-
GeneReviews lists brachydactyly as common to both TD subtypes.
- category: Neurological
name: Hypotonia
description: Generalised hypotonia in the newborn period, common to both subtypes.
phenotype_term:
preferred_term: Hypotonia
term:
id: HP:0001252
label: Hypotonia
frequency: VERY_FREQUENT
evidence:
- reference: PMID:20301540
reference_title: Thanatophoric Dysplasia.
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Other features common to type 1 and type 2 include: short ribs, narrow thorax, relative macrocephaly, distinctive facial features, brachydactyly, hypotonia, and redundant skin folds along the limbs.
explanation: >-
GeneReviews lists hypotonia as common to both TD subtypes.
- category: Integumentary
name: Redundant skin folds along the limbs
description: >-
Excess skin folds over the shortened limbs, a consequence of soft-tissue growth
outpacing skeletal growth; common to both subtypes.
phenotype_term:
preferred_term: Redundant skin
term:
id: HP:0001582
label: Redundant skin
frequency: VERY_FREQUENT
evidence:
- reference: PMID:20301540
reference_title: Thanatophoric Dysplasia.
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Other features common to type 1 and type 2 include: short ribs, narrow thorax, relative macrocephaly, distinctive facial features, brachydactyly, hypotonia, and redundant skin folds along the limbs.
explanation: >-
GeneReviews lists redundant skin folds along the limbs as common to both TD
subtypes.
- category: Skeletal
name: Platyspondyly
description: >-
Marked flattening of the vertebral bodies, a consistent radiographic finding.
phenotype_term:
preferred_term: Platyspondyly
term:
id: HP:0000926
label: Platyspondyly
evidence:
- reference: PMID:42547059
reference_title: >-
Thanatophoric dysplasia: prevalence, clinical characteristics, and molecular
findings in a public hospital from Western Mexico.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Phenotype: short stature, macrocephaly, hypotonia, distinctive facial features, narrow thorax, prominent abdomen, micromelia, redundant skinfolds, trident hand, short ribs, rhizomelic shortening, irregular metaphyses, platyspondyly and bowed femurs.
explanation: >-
Platyspondyly is listed in the phenotype summary of a consecutive TD birth
series. `frequency` is deliberately omitted: the series reports the feature list
without per-feature counts, so no band can be justified.
- category: Respiratory
name: Respiratory insufficiency
description: >-
Respiratory failure from the restrictive thorax, the immediate cause of death in
the great majority of affected infants.
phenotype_term:
preferred_term: Respiratory insufficiency
term:
id: HP:0002093
label: Respiratory insufficiency
frequency: VERY_FREQUENT
evidence:
- reference: PMID:20301540
reference_title: Thanatophoric Dysplasia.
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Most affected infants die of respiratory insufficiency shortly after birth. Rare long-term survivors have been reported.
explanation: >-
GeneReviews states that respiratory insufficiency is the cause of death in most
affected infants, supporting both the phenotype and the VERY_FREQUENT band.
histopathology:
- name: Disordered growth-plate ossification with chondrocyte hyperplasia
description: >-
Fetal long-bone sections show disordered ossification with centrally located
loosely structured osteoid, chondrocyte hyperplasia and failure of the normal
columnar organisation of the proliferative zone.
evidence:
- reference: PMID:39778871
reference_title: >-
An immunohistochemical study of thanatophoric dysplasia type 1 after fetus
autopsy examination.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Bone sections displayed disordered ossification, centrally located loosely structured osteoid, chondrocyte hyperplasia, and incomplete column formation, with reactive chondrocytes and foci resembling bone marrow in areas with incipient or no apparent ossification.
explanation: >-
Direct human fetal-autopsy histology of the growth plate in genetically confirmed
TD1, describing the disordered ossification and loss of column formation.
notes: >-
Reported from a single 17-week TD1 fetal autopsy (R248C). Curated at the root
because the finding is a growth-plate consequence shared by both subtypes, but the
published observation is TD1-only and n=1.
diagnosis:
- name: Prenatal ultrasound recognition
description: >-
TD is usually first recognised prenatally, on ultrasound showing severe shortening
of all long bones with a narrow thorax and relative macrocephaly. Prenatal
ultrasound is sufficient to drive management decisions but does not by itself
separate TD from the other lethal skeletal dysplasias.
diagnosis_term:
preferred_term: ultrasound imaging
term:
id: NCIT:C17230
label: Ultrasound Imaging
evidence:
- reference: PMID:20301540
reference_title: Thanatophoric Dysplasia.
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Prenatal diagnosis is possible by ultrasound examination and molecular genetic testing.
explanation: >-
GeneReviews states the two prenatal diagnostic modalities for TD as a whole.
- reference: PMID:39778871
reference_title: >-
An immunohistochemical study of thanatophoric dysplasia type 1 after fetus
autopsy examination.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
The decision was based on ultrasonographic examination showing pronounced shortening of all long bones with a characteristic curvature of the femur, without evidence of heredity.
explanation: >-
A worked example of the ultrasound findings that trigger the diagnosis, including
the femoral curvature that points towards TD1 specifically.
- name: Clinical and radiographic diagnosis
description: >-
The diagnosis is established on characteristic clinical and radiologic features —
micromelia, short ribs and narrow thorax, platyspondyly, and the femur and skull
shape that separate the subtypes — and/or on molecular confirmation. Radiography
is what assigns TD1 (curved femurs) versus TD2 (straight femurs with cloverleaf
skull).
diagnosis_term:
preferred_term: radiograph imaging procedure
term:
id: NCIT:C38101
label: X-Ray Imaging
evidence:
- reference: PMID:20301540
reference_title: Thanatophoric Dysplasia.
supports: SUPPORT
evidence_source: OTHER
snippet: >-
The diagnosis of TD is established in a proband with characteristic clinical and/or radiologic features and/or a heterozygous pathogenic variant in FGFR3 identified on molecular genetic testing.
explanation: >-
GeneReviews states the diagnostic criteria for TD as a whole, giving clinical,
radiologic and molecular routes.
- reference: PMID:39778871
reference_title: >-
An immunohistochemical study of thanatophoric dysplasia type 1 after fetus
autopsy examination.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
The X-rays validated the gross findings, emphasizing abnormalities in the long bones of the extremities and the skull.
explanation: >-
Confirms radiography as the modality that validates the skeletal findings in
practice, including at postmortem examination.
- name: Molecular confirmation of FGFR3 variant
description: >-
Molecular testing confirms the clinical and radiological diagnosis, distinguishes
TD from the other lethal chondrodysplasias, and assigns the subtype. A single
multiplexed PCR plus single-nucleotide-extension assay covers 14 recurrent FGFR3
changes accounting for 99% of TD1 and TD2 together — including the technically
awkward adjacent stop-codon changes in exon 18 — so one reaction serves both
subtypes with a shorter turnaround than Sanger or next-generation sequencing. This
shared single-assay diagnostic pathway is a root-level property of TD: it is
defined over the union of the subtypes, not over either one.
diagnosis_term:
preferred_term: genetic testing
term:
id: NCIT:C15709
label: Genetic Testing
evidence:
- reference: PMID:39357670
reference_title: >-
A Single Multiplex PCR and Single-Nucleotide Extension Assay for the Detection
of Common Thanatophoric Dysplasia I and II Mutations.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
We developed a single multiplexed PCR and a single-nucleotide extension (SNE) assay to identify 14 common mutations causing 99% of TD I and TD II, including the challenging three adjacent mutations in the stop codon of exon 18 of the FGFR3 gene.
explanation: >-
Establishes that one assay covers both TD subtypes at 99% of cases — the
technical basis for treating molecular confirmation as a single TD-level
diagnostic step rather than two subtype-specific ones.
- reference: PMID:39357670
reference_title: >-
A Single Multiplex PCR and Single-Nucleotide Extension Assay for the Detection
of Common Thanatophoric Dysplasia I and II Mutations.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Mutation analysis provides confirmation of a clinical and radiological diagnosis of thanatophoric dysplasia types I and II (TD I and II).
explanation: >-
States the role of molecular testing as confirmatory of the clinical and
radiological diagnosis, for both subtypes.
- reference: PMID:42547059
reference_title: >-
Thanatophoric dysplasia: prevalence, clinical characteristics, and molecular
findings in a public hospital from Western Mexico.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Molecular analysis allows to distinguish it from other lethal chondrodysplasias and to provide appropriate genetic counseling.
explanation: >-
States the clinical purpose of molecular confirmation — separating TD from the
other lethal chondrodysplasias and enabling counselling.
differential_diagnoses:
- name: Homozygous achondroplasia
description: >-
Biallelic FGFR3 p.Gly380Arg produces a lethal short-limb phenotype closely
resembling TD. The distinction is made molecularly (two copies of a weaker allele
versus one copy of a stronger one) and by parental phenotype, since both parents
of a homozygous-achondroplasia infant have achondroplasia while TD is essentially
always de novo to unaffected parents.
disease_term:
preferred_term: achondroplasia
term:
id: MONDO:0007037
label: achondroplasia
distinguishing_features:
- >-
Two affected parents and biallelic G380R on molecular testing, versus unaffected
parents and a single strongly activating de novo FGFR3 allele in TD. See
`Achondroplasia.yaml`.
evidence:
- reference: PMID:8640234
reference_title: >-
Graded activation of fibroblast growth factor receptor 3 by mutations causing
achondroplasia and thanatophoric dysplasia.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Homozygous achondroplasia resembles the phenotype of TD.
explanation: >-
States the phenotypic overlap that makes homozygous achondroplasia the principal
FGFR3-internal differential for TD.
- name: Other lethal chondrodysplasias
description: >-
Fibrochondrogenesis, achondrogenesis, the short-rib polydactyly syndromes and
osteogenesis imperfecta type II all present prenatally with severe micromelia and a
narrow thorax and are not reliably separable from TD on ultrasound alone. FGFR3
molecular analysis is what resolves them.
distinguishing_features:
- >-
Identification of a recurrent activating FGFR3 variant establishes TD and excludes
the collagen-, cilium- and matrix-related lethal dysplasias.
evidence:
- reference: PMID:42547059
reference_title: >-
Thanatophoric dysplasia: prevalence, clinical characteristics, and molecular
findings in a public hospital from Western Mexico.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Molecular analysis allows to distinguish it from other lethal chondrodysplasias and to provide appropriate genetic counseling.
explanation: >-
States directly that molecular analysis is the step that separates TD from the
other lethal chondrodysplasias.
genetic:
- name: FGFR3
gene_term:
preferred_term: FGFR3
term:
id: hgnc:3690
label: FGFR3
relationship_type: CAUSATIVE
variant_origin: DE_NOVO
presence: Heterozygous activating variant in essentially all cases
association: >-
Heterozygous gain-of-function FGFR3 variants cause both TD subtypes. The subtypes
are separated by which functional domain the change lies in: extracellular and
juxtamembrane cysteine-creating changes plus the exon-18 stop-codon extensions in
TD1, and the single recurrent kinase-domain K650E change in TD2. Per-allele detail
is curated in the subtype entries.
evidence:
- reference: PMID:7773297
reference_title: >-
Thanatophoric dysplasia (types I and II) caused by distinct mutations in
fibroblast growth factor receptor 3.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
A sporadic mutation causing a Lys650Glu change in the tyrosine kinase domain
of FGFR3 was found in 16 of 16 individuals with one type of TD. Of 39
individuals with a second type of TD, 22 had a mutation causing an Arg248Cys
change and one had a Ser371Cys substitution, both in the extracellular region of
the protein.
explanation: >-
The founding series establishing FGFR3 as the gene for both TD subtypes and
showing the domain split between them.
- reference: PMID:20301540
reference_title: Thanatophoric Dysplasia.
supports: SUPPORT
evidence_source: OTHER
snippet: >-
The diagnosis of TD is established in a proband with characteristic clinical and/or radiologic features and/or a heterozygous pathogenic variant in FGFR3 identified on molecular genetic testing.
explanation: >-
GeneReviews confirms heterozygous FGFR3 as the molecular basis of TD as a whole.
notes: >-
ClinGen has no Gene-Disease Validity assertion for FGFR3-thanatophoric dysplasia in
the locally cached ClinGen set (checked 2026-08), although the Skeletal Disorders
GCEP has curated FGFR3 as Definitive for achondroplasia and for hypochondroplasia
and Moderate for SADDAN. MONDO nonetheless records FGFR3 as the causal gene for
MONDO:0017042 via RO:0004003, and credits ClinGen for the exact synonym
"FGFR3-related thanatophoric dysplasia".
treatments:
- name: Comfort-focused and supportive perinatal care
action_category: THERAPEUTIC
description: >-
Because most affected infants die in the perinatal period from multisystem
complications, management goals are set with the family and commonly focus on
comfort care. Infants who are to be supported require long-term respiratory
support, typically tracheostomy and ventilation. Anaesthetic guidelines for
skeletal dysplasias apply. Other measures in long-term survivors include shunting
for hydrocephalus, suboccipital decompression for craniocervical-junction
constriction, anti-seizure medication and hearing aids.
treatment_term:
preferred_term: supportive care
term:
id: NCIT:C15747
label: Supportive Care
therapeutic_modality: OTHER
target_mechanisms:
- target: Thoracic Insufficiency and Pulmonary Hypoplasia
treatment_effect: BYPASSES
description: >-
Tracheostomy and long-term ventilation substitute for the chest-wall excursion
the restrictive thorax cannot provide; they bypass the mechanical limitation
rather than altering the skeletal lesion that causes it.
evidence:
- reference: PMID:20301540
reference_title: Thanatophoric Dysplasia.
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Newborns require long-term respiratory support (typically with tracheostomy and ventilation) to survive.
explanation: >-
Identifies the respiratory-support intervention as acting on the thoracic
insufficiency node, and as a prerequisite for survival rather than a cure.
evidence:
- reference: PMID:20301540
reference_title: Thanatophoric Dysplasia.
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Management goals should be established with the family and may focus on provision of comfort care.
explanation: >-
GeneReviews states the default management framing for TD as a whole.
- reference: PMID:20301540
reference_title: Thanatophoric Dysplasia.
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Other treatment measures may include shunt placement for hydrocephalus, suboccipital decompression for relief of craniocervical junction constriction, anti-seizure medication to control seizures, and hearing aids.
explanation: >-
Enumerates the supportive interventions relevant to long-term survivors.
- name: Vosoritide (off-label, single case report)
action_category: THERAPEUTIC
description: >-
Vosoritide is a C-type natriuretic peptide analogue that counteracts FGFR3
overactivation and is approved for achondroplasia, not for thanatophoric dysplasia.
Its use in TD rests on a SINGLE off-label case report (n = 1): a 9-year-old
long-term TD1 survivor treated for 28 months, in whom growth velocity and lung
vital capacity improved and foramen magnum stenosis did not radiologically
progress. This is one uncontrolled observation in an exceptional survivor and must
not be read as evidence of benefit in TD generally, still less as altering the
perinatal lethality that defines the disorder. The authors themselves call for
larger studies.
treatment_term:
preferred_term: Pharmacotherapy
term:
id: NCIT:C15986
label: Pharmacotherapy
therapeutic_agent:
- preferred_term: vosoritide
term:
id: NCIT:C152918
label: Vosoritide
therapeutic_modality: PEPTIDE
evidence:
- reference: PMID:41078071
reference_title: "Thanatophoric Dysplasia Type 1 Treated with Vosoritide: A Case Report."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
We report the response to vosoritide therapy in a 9-year-old girl with genetically confirmed TD1 (c.2420G>T).
explanation: >-
Establishes the scope of the evidence base: one patient, off-label. Recorded as
PARTIAL because a single uncontrolled case cannot establish efficacy.
- reference: PMID:41078071
reference_title: "Thanatophoric Dysplasia Type 1 Treated with Vosoritide: A Case Report."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Vosoritide was well tolerated and improved growth velocity and lung function in this long-term TD1 survivor, suggesting therapeutic potential even in severe FGFR3 overactivation. Given TD1's rarity, larger studies and further off-label experience are essential to validate these findings.
explanation: >-
The authors' own conclusion, including their explicit statement that the finding
requires validation. Quoted in full so the caveat travels with the claim.
- reference: PMID:41078071
reference_title: "Thanatophoric Dysplasia Type 1 Treated with Vosoritide: A Case Report."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Thanatophoric dysplasia type 1 (TD1) is the most severe form of FGFR3-related skeletal dysplasia, with high perinatal mortality and no approved pharmacologic therapies.
explanation: >-
Confirms that there is no approved pharmacologic therapy for TD, which is the
context that makes this single case report notable rather than authoritative.
notes: >-
Deliberately NOT linked to a pathophysiology node by `target_mechanisms`. The
CNP-NPR2 counter-regulatory target is curated in the
`fgfr_gain_of_function_skeletal_dysplasia` module and exercised in
`Achondroplasia.yaml`; asserting a mechanism edge here on the strength of one
off-label case would overstate what has been shown in TD.
discussions:
- discussion_id: td_root_disease_vs_grouping
kind: INTERPRETATION
status: RESOLVED
prompt: >-
Should thanatophoric dysplasia (MONDO:0017042) be modelled as a root `Disease`
with `has_subtypes` for TD1 and TD2, or as a `Grouping` over the two existing
standalone subtype entries?
rationale: >-
Resolved in favour of a root `Disease` with `has_subtypes`, on three grounds.
First, tooling. `build_coverage_index()` in
`src/dismech/compare/mondo_priority.py` calls `iter_disease_files()`, which globs
`kb/disorders/*.yaml` only and never reads `kb/groupings/`; coverage is counted
from `disease_term`, `has_subtypes[].subtype_term`, and `mappings.mondo_mappings`
restricted to `skos:exactMatch`/`skos:narrowMatch`. A `Grouping` alone would
therefore leave MONDO:0017042 permanently on the MONDO curation queue no matter
how well curated it was. This was verified by reading the source, not assumed.
Second, redundancy. `kb/groupings/FGFR_Related_Skeletal_Dysplasias.yaml` already
unions TD1 and TD2 with nine other FGFR members under a NECESSARY_AND_SUFFICIENT
`CONFORMS_TO_MODULE` criterion; a second grouping over just TD1 and TD2 would
duplicate that machinery while adding only the pair restriction, which
`has_subtypes` expresses more directly. Third, substance. Several TD claims are
reported for TD as a whole and have no natural home on either subtype: the birth
prevalence (PMID:18698630, PMID:42547059, PMID:7773297), the single molecular
assay covering 99% of both subtypes in one reaction (PMID:39357670), and the
GeneReviews "features common to type 1 and type 2" list (PMID:20301540). TD1's own
prevalence block currently has to label the overall-TD figure a population proxy
for TD1; this entry gives that claim a home without the proxy caveat. The
counter-argument — that a Disease root duplicates content held in the two subtype
entries — is addressed by keeping the root deliberately thin: three
pathophysiology nodes, two of which are `conforms_to` anchors on the FGFR module,
and no re-derivation of receptor biology or the growth-plate cascade. Precedent
for the alternative shape exists (`kb/groupings/Diabetes_Mellitus.yaml` maps
MONDO:0005015 with `skos:closeMatch` so a retained umbrella Disease can keep it as
`disease_term`), but that pattern exists to let a Grouping coexist with an umbrella
Disease, not to replace one.
resolution_note: >-
Curated as a root `Disease` (this entry). The pre-existing
`FGFR_Related_Skeletal_Dysplasias` grouping is left unchanged and continues to
carry TD1 and TD2 as members in their own right. Consequence a reviewer should
weigh: because this entry conforms to
`fgfr_gain_of_function_skeletal_dysplasia#Constitutive FGFR Activation`, `just
check-groupings kb/groupings/FGFR_Related_Skeletal_Dysplasias.yaml` now reports
"Thanatophoric Dysplasia" as an advisory candidate member of that grouping. It was
deliberately NOT added: the grouping's rationale describes members that differ in
receptor paralog and activating variant, and listing the root alongside its own two
subtypes would make the union overlap itself. Whether an N&S grouping should admit
a root whose subtypes it already lists is a grouping-design question, not a
curation defect in this entry.
posed_by: dismech curation (issue #8889)
posed_date: '2026-08-19T00:00:00Z'
resolved_date: '2026-08-19T00:00:00Z'
- discussion_id: td_root_thoracic_node_not_module_anchored
kind: OPEN_QUESTION
status: OPEN
prompt: >-
Should the thoracic-insufficiency and pulmonary-hypoplasia step be factored into
the `fgfr_gain_of_function_skeletal_dysplasia` module, or does it belong only to
the lethal members of the FGFR3 allelic series?
attaches_to:
- pathophysiology#Thoracic Insufficiency and Pulmonary Hypoplasia
rationale: >-
The node is left unanchored here on purpose. Achondroplasia and hypochondroplasia
share every upstream node in the module and do not reach thoracic insufficiency, so
adding it to the module would assert a consequence that most conformers do not
manifest. Adding it as a conditional or branch node is possible but would need an
explicit severity gate, and no such gating convention is established in the module
today. Flagged rather than acted on, since it is a module-level design change
outside the scope of curating this entry.
posed_by: dismech curation (issue #8889)
posed_date: '2026-08-19T00:00:00Z'
- discussion_id: td_vosoritide_single_case
kind: KNOWLEDGE_GAP
status: OPEN
prompt: >-
Does CNP-analogue therapy affect the mechanisms that make thanatophoric dysplasia
lethal, as opposed to affecting linear growth in an exceptional survivor?
rationale: >-
The only TD treatment evidence beyond supportive care is a single off-label
vosoritide case report in a 9-year-old TD1 survivor (PMID:41078071). Perinatal
lethality in TD is set by thoracic dimensions established in utero, and no
postnatal growth-directed therapy has been shown to address that. Whether the
reported vital-capacity improvement reflects any change in the underlying thoracic
restriction, or simply somatic growth in a patient who had already survived the
lethal window, is unresolved on a single case.
proposed_experiments:
- experiment_id: exp_td_cnp_analogue_survivor_registry
name: Multi-patient registry of CNP-analogue therapy in long-term TD survivors
description: >-
Prospective registry capture of growth velocity, thoracic circumference, forced
vital capacity and foramen magnum imaging in long-term TD survivors receiving
off-label CNP-analogue therapy, using each patient's pre-treatment trajectory as
their own control, since a randomized comparison is not feasible at this rarity.
posed_by: dismech curation (issue #8889)
posed_date: '2026-08-19T00:00:00Z'
notes: >
Scope. This entry is deliberately thin. It carries only claims made about
thanatophoric dysplasia as a whole: TD-level birth prevalence, the shared diagnostic
pathway, the allelic-series framing, the TD1/TD2 discriminator, and the
thoracic-insufficiency lethality step. The FGFR3 receptor biology and the
growth-plate cascade are curated once in
`kb/modules/fgfr_gain_of_function_skeletal_dysplasia.yaml`, and per-allele,
per-subtype detail lives in `Thanatophoric_Dysplasia_Type_1.yaml` and
`Thanatophoric_Dysplasia_Type_2.yaml`. Related FGFR3 points on the same severity
gradient: `Hypochondroplasia.yaml`, `Achondroplasia.yaml`, `SADDAN.yaml`, and the
craniosynostosis outliers `Crouzon_Syndrome_with_Acanthosis_Nigricans.yaml` and
`Muenke_Syndrome.yaml`.
Sources not usable at curation time. Orphanet ORPHA:2655, which MONDO:0017042 xrefs
and which would supply a quotable definition and epidemiology table, could not be
cached: `just refresh-orphadata` fails with a sha256 mismatch against the pinned
`data/orphadata/MANIFEST.yaml` because upstream Orphadata has drifted, and re-pinning
the manifest would rebuild every `references_cache/ORPHA_*.md` in the repository,
which is out of scope here. Separately, no ClinGen Gene-Disease Validity assertion
exists for FGFR3-thanatophoric dysplasia in the cached ClinGen set.
Deep research. No new deep-research provider pass was run for this entry. Six
pre-existing TD1/TD2 deep-research reports under `research/` were available as leads.
Because no deep-research report drives any claim here, `just preflight-dr` is not
applicable; Named Entity Confusion discipline was applied manually by confirming that
every cited abstract concerns FGFR3 thanatophoric dysplasia rather than another
lethal skeletal dysplasia or a milder FGFR3 allelic sibling.
references:
- reference: PMID:20301540
title: Thanatophoric Dysplasia.
tags:
- GeneReviews
findings:
- statement: Defines TD as a whole and enumerates the features common to type 1 and type 2
- statement: >-
Gives the TD1 (bowed femurs, uncommon craniosynostosis) versus TD2 (straight
femurs, uniform cloverleaf skull) discriminator
- statement: Autosomal dominant, de novo in the majority of probands
- reference: PMID:8640234
title: >-
Graded activation of fibroblast growth factor receptor 3 by mutations causing
achondroplasia and thanatophoric dysplasia.
findings:
- statement: TD alleles activate FGFR3 more strongly than the achondroplasia G380R allele
- statement: >-
All the alleles tested constitutively activate the receptor in a
ligand-independent manner
- reference: PMID:7773297
title: >-
Thanatophoric dysplasia (types I and II) caused by distinct mutations in
fibroblast growth factor receptor 3.
findings:
- statement: K650E accounts for TD2 in 16 of 16 individuals
- statement: TD1 and TD2 arise from mutations in different FGFR3 functional domains
- reference: PMID:39357670
title: >-
A Single Multiplex PCR and Single-Nucleotide Extension Assay for the Detection of
Common Thanatophoric Dysplasia I and II Mutations.
findings:
- statement: >-
One assay detects 14 FGFR3 changes accounting for 99% of TD1 and TD2 combined
- reference: PMID:42547059
title: >-
Thanatophoric dysplasia: prevalence, clinical characteristics, and molecular
findings in a public hospital from Western Mexico.
findings:
- statement: TD birth prevalence 0.85 per 10,000 (95% CI 0.32-1.37) in Western Mexico
- statement: All ten ascertained cases were TD1 and sporadic
- reference: PMID:18698630
title: >-
The population-based prevalence of achondroplasia and thanatophoric dysplasia in
selected regions of the US.
findings:
- statement: US TD birth prevalence 0.21-0.30 per 10,000 livebirths
- statement: TD is one-third to one-half as frequent as achondroplasia
- reference: PMID:39778871
title: >-
An immunohistochemical study of thanatophoric dysplasia type 1 after fetus autopsy
examination.
findings:
- statement: >-
Fetal-autopsy histology of disordered growth-plate ossification and lung
immaturity in genetically confirmed TD1
- reference: PMID:41078071
title: "Thanatophoric Dysplasia Type 1 Treated with Vosoritide: A Case Report."
findings:
- statement: >-
Single off-label vosoritide case in a long-term TD1 survivor; not evidence of
benefit in TD generally