Defects in Nuclear Proteins and Transcription Factors

Slide 1 · Defects in nuclear proteins and transcription factors

A developmental defect in gene regulation can alter the shape, identity, and number of skeletal elements.

Genes discussed in the skeletal chapter encode transcription factors—not structural bone matrix proteins.

The phenotype depends on where and when the factor directs developmental programs.

A single gene can influence multiple organs, making associated findings diagnostic.

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Use the affected structure and extra-skeletal clues to infer the disrupted developmental regulator.

Distinguish dysostosis from skeletal dysplasia and explain mesenchymal patterning.

Connect six named transcription factors with the defining clinical syndromes.

Apply morphology, organ-system associations, and appropriate genetic testing to cases.

Slide 3 · Developmental anomalies: Two organizing terms

Location and distribution help classify congenital skeletal abnormalities.

Dysostosis

Abnormal individual skeletal elements

Regional or patterned malformations

Example: Absent or abnormal digit

Skeletal dysplasia

More widespread skeletal growth disorder

Can affect axial and appendicular skeleton

Example: Generalized chondrocyte dysfunction

Slide 4 · Mesenchymal condensation is an early control point

Patterning errors arise before the mature shape of a bone is recognizable.

Mesenchyme

Regional condensation

Skeletal precursor

Mature element

Mesenchymal cells aggregate at future skeletal sites.

Selected condensations adopt a chondrogenic or osteogenic developmental program.

Loss of spatial control can produce missing, fused, duplicated, or malformed skeletal parts.

Slide 5 · Two routes to a mature skeletal element

Skeletal morphogenesis depends on specification followed by tissue differentiation.

Intramembranous

Mesenchymal cells → osteoblasts

Important in skull vault and clavicle

RUNX2 is required for osteogenesis

Endochondral

Mesenchymal cells → cartilage model

Chondrocyte growth and maturation

SOX9 regulates chondrogenesis

Slide 6 · A transcription factor is not a structural scaffold

Gene-regulatory proteins act upstream of the tissue phenotype.

DNA regulator

Gene expression

Cell fate / differentiation

Skeletal pattern

A transcription factor recognizes regulatory DNA or works in a transcriptional complex.

Its downstream targets control lineage commitment, differentiation, and tissue architecture.

The phenotype reflects altered gene expression, not necessarily loss of a bone matrix protein.

Slide 7 · Developmental timing explains persistent malformation

Congenital patterning errors cannot be interpreted as ordinary adult remodeling defects.

Pattern formation

Ossification

Postnatal growth

Adult remodeling

Embryonic specification determines whether a skeletal part forms and where it lies.

Postnatal growth changes the dimensions of an established skeletal template.

Adult remodeling maintains tissue balance but cannot recreate absent developmental structures.

Slide 8 · Why one regulator may affect multiple organs

Developmental transcription factors often have context-dependent roles.

Shared regulator

Skeletal phenotype

Extra-skeletal phenotype

A shared gene may participate in limb, heart, kidney, eye, pigmentation, or gonadal pathways.

Distribution of abnormalities can be more informative than any single skeletal sign.

Syndromic evaluation must include clinically relevant non-skeletal structures.

Slide 9 · The six gene–phenotype associations

The chapter groups six clinically distinctive developmental disorders under transcription-factor defects.

Gene

Associated disorder

Hallmark phenotype

HOXD13

Brachydactyly D/E

Digits and hand/foot rays

RUNX2

Cleidocranial dysplasia

Skull, clavicles, teeth

SOX9

Campomelic dysplasia

Cartilage, long bones, sex development

TBX5

Holt–Oram syndrome

Upper limbs and heart

LMX1B

Nail–patella syndrome

Nails, patellae, kidney

PAX3

Waardenburg types I/III

Hearing, pigment, craniofacial ± limbs

Slide 10 · Read a phenotype anatomically

Identify the predominant affected site before assigning a syndrome.

Site of anomaly

Pattern of bones

Non-skeletal signs

Gene hypothesis

Distal digits → consider HOXD13-associated patterning defects.

Cranium, clavicles, and dentition → prioritize RUNX2-related disorder.

Long bones, forelimbs, patellae, or craniofacial features direct different gene hypotheses.

Slide 11 · HOXD13 directs distal limb patterning

The anatomical distribution of shortening is central to this diagnosis.

HOXD13 variation

Altered limb pattern

Selective skeletal shortening

HOXD13 encodes a homeobox transcription factor involved in limb patterning.

Specific pathogenic variants can alter formation of digits and the smaller long bones of hands and feet.

The same gene can produce different, partially overlapping limb phenotypes.

Slide 12 · Brachydactyly requires skeletal localization

Short digits may result from different bones being short.

Phalangeal

Digit segment is short

Type D emphasizes the thumb distal phalanx

Metacarpal / metatarsal

Metacarpal or metatarsal is short

Type E emphasizes short rays

Slide 13 · Brachydactyly type D: The thumb tip

Type D is defined by a short, broad distal phalanx of the thumb.

Distal thumb phalanx

Short + broad

Type D phenotype

The nail-bearing distal thumb segment is the primary affected element.

This clinical label describes morphology; It is not specific to one pathogenic variant.

HOXD13-associated families may show overlapping D-like abnormalities.

Slide 14 · Brachydactyly type E: Short metapodials

Type E is characterized by short metacarpals and/or metatarsals.

Short metacarpal(s)

± short metatarsal(s)

Type E phenotype

Hand and foot rays may be unequally affected or asymmetrical.

Distal phalanx anomalies can coexist but do not define type E.

This precise distinction corrects ambiguity in the supplied chapter’s abbreviated description.

Slide 15 · Type D versus type E: Identify the short bone

Do not classify a short digit without examining which segment is reduced.

Type D — distal thumb phalanx

Proximal → distal phalanx

Short, broad distal phalanx

Type E — metacarpal

Metacarpal → proximal → distal

Short metacarpal or metatarsal

Slide 16 · HOXD13 produces an allelic phenotype spectrum

One developmental regulator can cause different skeletal patterns.

HOXD13 pathogenic variant

Pattern-specific gene effects

Variable limb morphology

Published variants are associated with brachydactyly and synpolydactyly.

Phenotypic effects can vary within a family and between limbs.

The gene association does not mean all forms of brachydactyly are HOXD13-related.

Slide 17 · Variant mechanism is not always simple loss of function

Different substitutions can change sequence-specific DNA interactions.

Variant type

Regulatory effect

Digit/ray phenotype

HOXD13 homeodomain missense variants have shown altered DNA-binding properties in vitro.

Polyalanine expansions and other variants have distinct genotype–phenotype associations.

Clinical morphology cannot reliably identify a specific variant on its own.

Slide 18 · Brachydactyly: Diagnostic reasoning

First establish whether the anomaly is isolated or part of a syndrome.

Define bone affected

Check distribution

Assess family history

Targeted genetic workup

Inspect both hands and feet, including the specific bony elements affected.

Ask about similar familial limb findings; Expressivity may vary.

Molecular testing is guided by the pattern rather than the label “short fingers” alone.

Slide 19 · RUNX2 is central to osteoblast differentiation

RUNX2 is needed to generate osteogenic tissue during skeletal formation.

RUNX2 activity

Osteoblast differentiation

Skull / clavicle development

Its transcriptional activity participates in osteoblast differentiation and skeletal morphogenesis.

The skull and clavicles show conspicuous consequences when RUNX2 activity is deficient.

Dental development also depends on the associated developmental program.

Slide 20 · RUNX2 loss of function: Cleidocranial dysplasia

The defining syndrome couples cranial, clavicular, and dental abnormalities.

Reduced RUNX2 function

Deficient ossification

Cranial + clavicular + dental signs

Autosomal dominant inheritance with RUNX2 loss of function.

The classic triad is delayed cranial suture closure, abnormal clavicles, and dental anomalies.

Expression ranges from full skeletal involvement to mild or predominantly dental disease.

Slide 21 · Clavicular dysplasia: A distinctive structural clue

The clavicles may be hypoplastic, discontinuous, or absent.

Abnormal clavicle formation

Altered shoulder-girdle support

Hypermobile shoulder position

Clavicular abnormality is often bilateral but need not be symmetrical.

Shoulders may be unusually mobile when clavicles are severely deficient.

The finding has greater specificity in combination with cranial and dental signs.

Slide 22 · Open fontanelles and cranial sutures

Delayed skull ossification leaves sites of membranous separation persistent.

RUNX2 deficiency

Delayed skull ossification

Patent sutures / fontanelles

Fontanelles may remain patent beyond the usual period of closure.

Cranial sutures can be conspicuously wide or remain open.

Imaging findings should be read together with clavicular and dental abnormalities.

Slide 23 · Wormian bones are accessory sutural bones

Small additional ossicles may develop within cranial sutures.

Altered sutural ossification

Accessory sutural ossicles

Wormian bones

Wormian bones are one recognized radiographic sign of cleidocranial dysplasia.

They represent altered cranial ossification architecture.

They are not individually diagnostic without the larger phenotype.

Slide 24 · Delayed eruption of permanent teeth

Dental delay can be a leading clinical presentation.

Disturbed dental development

Delayed eruption

Retained / impacted teeth

Primary teeth may be retained when permanent teeth fail to erupt on schedule.

Impacted permanent teeth and dental crowding may complicate eruption.

The dental phenotype should prompt inspection of the clavicles and skull.

Slide 25 · Supernumerary teeth refine the diagnosis

An excess of tooth germs is a strong supporting clue in the appropriate skeletal setting.

Additional tooth germs

Eruption obstruction

Characteristic dental pattern

Supernumerary teeth may be accompanied by impacted permanent teeth.

Dental panoramas help identify the number and position of unerupted teeth.

The combination with open sutures and clavicular hypoplasia strongly suggests RUNX2 dysfunction.

Slide 26 · Cleidocranial dysplasia: Recognize the triad

A three-organ structural constellation is more distinctive than short stature alone.

Cranium

Open or delayed sutures

Patent fontanelles

Wormian bones may occur

Clavicles

Hypoplasia / aplasia

Shoulder mobility may increase

Sometimes asymmetric

Dentition

Delayed permanent teeth

Supernumerary teeth

Impaction / malocclusion

Slide 27 · RUNX2 genotype and phenotype are variable

Residual transcriptional activity helps explain a phenotypic continuum.

RUNX2 functional change

Residual activity varies

Spectrum of features

Classic disease is commonly associated with reduced functional RUNX2 dosage.

Some alleles yield milder skeletal or predominantly dental manifestations.

Genetic interpretation requires clinical correlation; The variant alone does not quantify severity.

Slide 28 · Cleidocranial dysplasia: Diagnostic sequence

Clinical recognition is followed by imaging and molecular confirmation.

Clinical triad

Targeted radiographs

RUNX2 analysis

Examine cranial sutures, shoulder girdle, stature, and eruption of teeth.

Document the relevant skull, clavicle, and dental radiographic features.

Interpret RUNX2 molecular results in conjunction with family history and phenotype.

Slide 29 · Differential: Delayed cranial mineralization

Not every open fontanelle indicates a RUNX2-related disorder.

RUNX2-related CCD

Delayed eruption; Supernumerary teeth

Clavicular hypoplasia

Sutural patency

Hypophosphatasia pattern

Premature deciduous tooth loss

Generalized mineralization defect

Biochemical ALP is diagnostically relevant

Slide 30 · SOX9 governs chondrocyte differentiation

SOX9-dependent gene regulation is essential to the cartilage developmental program.

SOX9 activity

Chondrocyte differentiation

Cartilage architecture

SOX9 contributes to chondrocyte differentiation and cartilage matrix gene regulation.

Deficiency disrupts skeletal organization during early development.

Clinical outcomes extend beyond cartilage because SOX9 has other embryonic roles.

Slide 31 · Campomelic dysplasia: The skeletal pattern

Long-bone bowing and shortening are key manifestations.

Altered SOX9 function

Impaired cartilage formation

Bowed / short long bones

The disorder affects long-bone development and can produce markedly bowed limbs.

Clubfeet and other skeletal abnormalities may accompany the long-bone phenotype.

Characteristic craniofacial and airway findings strengthen suspicion.

Slide 32 · SOX9 also participates in testis determination

Sex-development findings reflect SOX9 function outside the skeleton.

SOX9 developmental activity

Skeletal differentiation

46,XY sex development

SOX9 acts downstream of SRY in testis developmental signaling.

Individuals with a 46,XY karyotype may have atypical or female external genitalia.

This association connects skeletal morphology with gonadal differentiation pathways.

Slide 33 · Airway compromise drives early clinical risk

In campomelic dysplasia, respiratory instability is clinically consequential.

Airway cartilage abnormality

Airway collapse / instability

Respiratory compromise

Laryngotracheomalacia and other airway abnormalities can cause severe respiratory compromise.

The risk differs mechanistically from a syndrome caused mainly by a very small rib cage.

Early airway evaluation is important when the phenotype is suspected.

Slide 34 · Campomelic dysplasia may lack obvious bowing

Absence of classic camptomelia does not exclude a SOX9-related disorder.

SOX9 disruption

Variable skeletal expression

Classic / acampomelic patterns

An acampomelic presentation is recognized in the SOX9 phenotypic spectrum.

Assessment should integrate airway, facial, skeletal, and sex-development findings.

Clinical genetics may be required when imaging is not archetypal.

Slide 35 · SOX9 disruption can involve noncoding regulation

A normal coding sequence is not the entire genetic explanation.

Upstream regulatory region

SOX9 expression

Developmental phenotype

Upstream chromosomal rearrangements can interrupt SOX9 regulatory elements.

Such changes may alter SOX9 expression while leaving coding exons intact.

Suspected cases may require assessment for structural/regulatory variants.

Slide 36 · Campomelic dysplasia: Integrated recognition

Skeletal dysplasia and non-skeletal findings form one developmental syndrome.

Skeletal

Short, bowed long bones

Clubfeet may occur

May be acampomelic

Airway / facial

Laryngotracheomalacia

Pierre Robin sequence

Cleft palate may occur

Sex development

46,XY DSD is possible

Variable genital phenotype

SOX9 pathway involvement

Slide 37 · TBX5 links upper-limb and cardiac development

Holt–Oram syndrome is a heart–hand disorder.

TBX5 function

Upper-limb morphogenesis

Heart development

TBX5 is a T-box transcription factor involved in upper-limb patterning.

The same developmental regulator participates in cardiac formation.

The coexistence of upper-limb and cardiac defects is diagnostically important.

Slide 38 · Holt–Oram: Upper-limb radial-ray abnormalities

Thumb, radius, and carpal structures are major examination targets.

TBX5 alteration

Upper-limb field defect

Thumb / radial-ray anomaly

An affected thumb may be hypoplastic, absent, or triphalangeal.

Radius and carpal abnormalities can extend the limb phenotype.

Upper-limb findings can be asymmetric; Lower-limb predominance suggests an alternative diagnosis.

Slide 39 · Holt–Oram: Congenital cardiac defects

An upper-limb malformation should trigger attention to heart anatomy.

TBX5-related cardiogenesis defect

Septal malformation

Cardiac evaluation

Atrial or ventricular septal defects are characteristic cardiac associations.

Cardiac structural abnormalities and limb anomalies may vary in severity independently.

An echocardiographic assessment is relevant to syndrome characterization.

Slide 40 · Conduction disease is a separate Holt–Oram clue

The cardiac phenotype extends beyond anatomical septal defects.

TBX5 alteration

Conduction system phenotype

ECG evaluation

Conduction abnormalities may occur with or without major structural cardiac disease.

Electrocardiographic assessment complements echocardiographic evaluation.

The combination of a radial-ray phenotype and conduction disease strengthens the gene hypothesis.

Slide 41 · Holt–Oram: Systematic phenotype recognition

Do not call every upper-limb anomaly Holt–Oram syndrome.

Upper limb

Thumb / radius / carpal anomaly

Unilateral or asymmetric possible

Typically preaxial structures

Cardiac anatomy

Septal defects are characteristic

Evaluate by echocardiography

Severity is variable

Cardiac conduction

Conduction disease may coexist

Evaluate by ECG

Requires independent assessment

Slide 42 · LMX1B links limb dorsal identity to organs

Nail–patella syndrome is a recognizable multi-system developmental disorder.

LMX1B dysfunction

Limb dorsal patterning

Renal / ocular effects

LMX1B participates in dorsal limb patterning.

The phenotype prominently affects nails, patellae, and elbows.

Podocyte and ocular consequences explain why a skeletal diagnosis needs renal and eye review.

Slide 43 · Nails are an accessible diagnostic sign

Nail abnormalities can reveal a broader underlying skeletal phenotype.

LMX1B patterning defect

Nail hypoplasia / dysplasia

Syndromic recognition

Nails may be hypoplastic, absent, ridged, or dystrophic.

The thumbs are often more conspicuously affected than other digits.

Examination should extend from nails to knee and elbow anatomy.

Slide 44 · Patellar abnormalities define the syndrome

The patellae may be small, dysplastic, unstable, or absent.

Altered limb pattern

Patellar hypoplasia / aplasia

Knee instability

Patellar deficiency may be associated with knee pain or instability.

Clinical examination can show restricted or abnormal knee mechanics.

Radiographs help characterize patellar morphology in context.

Slide 45 · Elbow and radial-head abnormalities

Nail–patella syndrome is not limited to the knee.

Elbow development altered

Radial-head malposition

Restricted movement

Elbow movement may be restricted, particularly pronation and supination.

Radial-head malposition and other elbow dysplasia may occur.

The nail–knee–elbow combination is a strong pattern-recognition triad.

Slide 46 · Iliac horns: A specific radiographic clue

Posterolateral iliac projections can support nail–patella syndrome.

LMX1B phenotype

Posterolateral iliac projections

Iliac horns

Iliac horns are bilateral bony projections from the iliac bones.

They are a distinctive radiographic feature when present.

They are not required for the diagnosis and should not replace systemic evaluation.

Slide 47 · Renal involvement can dominate long-term risk

Proteinuria may be an early manifestation of LMX1B-associated nephropathy.

LMX1B podocyte role

Proteinuria ± hematuria

Possible nephropathy

Kidney involvement may present with proteinuria, sometimes with hematuria.

Progression to chronic kidney disease is possible in some affected patients.

The extent of nail or patellar changes does not safely exclude renal disease.

Slide 48 · Eye findings broaden the LMX1B phenotype

Ocular surveillance is relevant even when skeletal signs lead to diagnosis.

LMX1B ocular development

Glaucoma / ocular hypertension

Ophthalmic assessment

Primary open-angle glaucoma and ocular hypertension occur more often in nail–patella syndrome.

The phenotype reflects LMX1B function beyond limb development.

Eye assessment and renal evaluation address different non-skeletal risks.

Slide 49 · Nail–patella: Combine musculoskeletal and organ clues

The syndrome requires an integrated phenotype rather than a single radiograph.

Limb signs

Nail dysplasia

Patellar aplasia / hypoplasia

Elbow abnormalities; Iliac horns

Kidney

Proteinuria ± hematuria

Progressive disease is possible

Requires separate renal assessment

Eye

Increased glaucoma risk

Possible ocular hypertension

Needs clinical ophthalmic review

Slide 50 · PAX3 affects neural-crest-associated phenotypes

Waardenburg syndrome links auditory and pigmentary development.

PAX3 change

Auditory–pigmentary development

Craniofacial ± limb findings

PAX3 encodes a developmental transcription factor with roles in early cell-lineage specification.

Phenotype centers on hearing, pigmentation, and craniofacial morphology.

The limb phenotype becomes especially important in Waardenburg type III.

Slide 51 · Waardenburg type I: Cardinal constellation

Hearing loss, pigment change, and dystopia canthorum form a key syndrome pattern.

PAX3-related development

Hearing + pigmentation

Dystopia canthorum

Congenital sensorineural hearing loss may be present.

Pigmentary variation may affect hair, irides, and skin.

Dystopia canthorum describes lateral displacement of the medial canthi.

Slide 52 · Waardenburg type III adds limb involvement

Type III combines Waardenburg features with upper-limb musculoskeletal anomalies.

Type I pattern

Additional limb abnormalities

Type III phenotype

Limb muscle hypoplasia, joint contractures, or hand anomalies can accompany the auditory–pigmentary signs.

Type I and III are related PAX3-associated phenotypes.

Limb defects should not be confused with TBX5-associated heart–hand syndrome.

Slide 53 · Waardenburg I versus III

The presence of upper-limb abnormalities shifts the differential.

Type I

Hearing and pigmentation phenotype

Dystopia canthorum is typical

No defining major limb pattern

Type III

Overlaps type I features

Limb muscle/joint abnormalities

May include carpal fusion or syndactyly

Slide 54 · From gene function to organ-specific findings

A developmental regulator leaves a recognizable anatomical signature.

Gene

Associated disorder

Hallmark phenotype

HOXD13

Brachydactyly D/E

Digits and hand/foot rays

RUNX2

Cleidocranial dysplasia

Skull, clavicles, teeth

SOX9

Campomelic dysplasia

Cartilage, long bones, sex development

TBX5

Holt–Oram syndrome

Upper limbs and heart

LMX1B

Nail–patella syndrome

Nails, patellae, kidney

PAX3

Waardenburg types I/III

Hearing, pigment, craniofacial ± limbs

Slide 55 · Most discriminating non-skeletal clues

Extra-skeletal findings can separate disorders with superficially similar limb defects.

Heart or airway

TBX5: Heart defects / conduction

SOX9: Unstable airway

Consider urgent associated risks

Kidney or eye

LMX1B: Proteinuria / glaucoma

Assess beyond limb shape

Do not infer renal status from nails

Hearing or dentition

PAX3: Hearing / pigmentation

RUNX2: Eruption + extra teeth

Combine findings with morphology

Slide 56 · Molecular diagnosis requires phenotype fit

Gene identification is most informative when the clinical pattern has been well defined.

Phenotype definition

Gene / panel choice

Variant interpretation

Clinical correlation

Use anatomy and associated organ abnormalities to prioritize plausible genes.

Different variant classes may alter dosage, DNA binding, or noncoding regulation.

A variant of uncertain significance is not itself a molecular diagnosis.

Slide 57 · Defects in regulators versus bone matrix

Different molecular classes can produce skeletal malformation by distinct routes.

Transcription-factor defect

Disrupted developmental pattern

Abnormal condensation or cell fate

Examples: RUNX2, SOX9, TBX5

Structural protein defect

Abnormal matrix composition/assembly

Bone/cartilage tissue fragility or growth

Examples: Type I or II collagen

Slide 58 · Case: Skull, clavicles, and permanent teeth

CLINICAL FINDINGS

A child has persistent cranial sutures, small clavicles, and numerous unerupted permanent teeth.

INTERPRETATION

Best syndromic diagnosis: Cleidocranial dysplasia.

Most likely regulator: RUNX2.

The diagnostic reasoning depends on the combined cranial–clavicular–dental pattern.

Slide 59 · Case: Bowed limbs and compromised airway

CLINICAL FINDINGS

A newborn has bowed long bones, Pierre Robin sequence, and airway instability.

INTERPRETATION

Best mechanistic hypothesis: SOX9-related campomelic dysplasia.

Assess for associated 46,XY sex-development findings when clinically relevant.

The airway problem can reflect tracheobronchomalacia, not solely thoracic narrowing.

Slide 60 · Case: Unusual nails, small patellae, proteinuria

CLINICAL FINDINGS

An adolescent has dystrophic nails, patellar hypoplasia, limited elbow movement, and proteinuria.

INTERPRETATION

Best syndrome: Nail–patella syndrome (LMX1B).

The renal finding is an important systemic manifestation, not an incidental skeletal symptom.

Include renal and ophthalmic review in clinical evaluation.

Slide 61 · Case: Abnormal thumb and an atrial septal defect

CLINICAL FINDINGS

A patient has a triphalangeal thumb and a congenital cardiac septal defect.

INTERPRETATION

Consider TBX5-related Holt–Oram syndrome.

Examine radial-ray and carpal elements; Assess ECG as well as cardiac structure.

A similar hand anomaly without the cardiac pattern has a broader differential.

Slide 62 · Case: Hearing loss, pigmentation, and limb contracture

CLINICAL FINDINGS

A child has congenital hearing loss, heterochromia, dystopia canthorum, and upper-limb contractures.

INTERPRETATION

Consider PAX3-related Waardenburg syndrome type III.

The extra limb feature distinguishes this presentation from a typical type I pattern.

PAX3-associated craniofacial and sensory findings support the syndromic diagnosis.

Slide 63 · Case: A short thumb tip versus short hand rays

CLINICAL FINDINGS

Two relatives have short digits; One has a broad thumb tip and the other has shortened metacarpals.

INTERPRETATION

Thumb-tip distal phalanx shortening is type D morphology.

Metacarpal shortening is type E morphology.

Overlapping HOXD13-related phenotypes make precise bone-level description essential.

Slide 64 · Consolidated gene–syndrome map

The involved transcription factor predicts an anatomical cluster rather than a single isolated sign.

Gene

Associated disorder

Hallmark phenotype

HOXD13

Brachydactyly D/E

Digits and hand/foot rays

RUNX2

Cleidocranial dysplasia

Skull, clavicles, teeth

SOX9

Campomelic dysplasia

Cartilage, long bones, sex development

TBX5

Holt–Oram syndrome

Upper limbs and heart

LMX1B

Nail–patella syndrome

Nails, patellae, kidney

PAX3

Waardenburg types I/III

Hearing, pigment, craniofacial ± limbs

Slide 65 · Final synthesis: Six distinct patterning signatures

Integrate site of skeletal malformation with sentinel organ findings.

HOXD13: Digits and rays; RUNX2: Skull–clavicle–teeth; SOX9: Cartilage, airway, sex development.

TBX5: Upper limb–heart; LMX1B: Nail–patella–kidney; PAX3: Pigment–hearing–craniofacial ± limb.

The biological lesson is altered embryonic gene regulation, not simply abnormal bone mineralization.

Slide 66 · Source and interpretation notes

Textbook core and independently checked condition-specific detail were kept distinguishable.

Primary: Robbins, Cotran & Kumar, Pathologic Basis of Disease, 11th ed. (2026), Ch 26, pp 1066–1068; Table 26.1.

Supplement: GeneReviews entries for RUNX2, SOX9, TBX5, LMX1B and PAX3; Johnson et al. for HOXD13.

Brachydactyly E is defined by short metacarpals/metatarsals in the supplemental genetics literature.