Orthopedic Manifestations of Genetic Disorders

Skeletal Dysplasias - Short & Brittle Tales

• Achondroplasia:

  • Genetics: FGFR3 gene mutation; Autosomal Dominant (AD), ~80% new mutations.
  • Patho: ↓ endochondral ossification.
  • Clinical: Rhizomelic (proximal) short stature, macrocephaly, frontal bossing, midface hypoplasia, trident hand.
  • Ortho: Genu varum, thoracolumbar kyphosis, lumbar spinal stenosis (adults).

    ⭐ Foramen magnum stenosis is critical; risk of cervicomedullary compression, apnea, sudden death.

  • Mgmt: Monitor development, neuro status. Vosoritide. Surgical: spinal decompression, limb lengthening.

• Osteogenesis Imperfecta (OI): "Brittle Bone Disease"

  • Genetics: COL1A1/A2 gene mutations (Type I collagen defect). AD common for Types I-IV.
  • Clinical: Fragile bones (recurrent fractures), blue sclera, hearing loss, dentinogenesis imperfecta (DI), joint laxity, short stature.
  • Ortho: Bowing deformities (long bones), scoliosis, basilar invagination.
  • Sillence Types (Key):
    • Type I: Mildest, blue sclera. Most common.
    • Type II: Perinatal lethal.
    • Type III: Progressive deforming, severe.
    • Type IV: Moderate, DI common, sclera normal/grey.
  • Mgmt: Bisphosphonates, telescopic rodding, fracture care, physio.

Connective Tissue Disorders - Flexibility & Frailty

Disorders of collagen and other connective tissue proteins, leading to joint hypermobility, skeletal abnormalities, and tissue fragility.

• Marfan Syndrome
  • Genetics: FBN1 gene mutation (Autosomal Dominant), affecting fibrillin-1.
  • Orthopedic Manifestations:
    • Tall stature, arachnodactyly (long, slender digits)
    • Pectus excavatum or carinatum
    • Scoliosis (>60% of patients), often progressive
    • Pes planus (flat feet), joint hypermobility
    • Protrusio acetabuli, dural ectasia
  • Diagnosis: Ghent criteria (systemic score, considering family history, genetic testing).
• Ehlers-Danlos Syndromes (EDS)
  • General: Group of inherited disorders affecting collagen synthesis/structure. Focus on hypermobile EDS (hEDS).
  • Orthopedic Manifestations (hEDS):
    • Joints: Significant generalized joint hypermobility (Beighton score ≥5/9); recurrent dislocations/subluxations (esp. shoulder, patella).
    • Pain & Degeneration: Chronic widespread musculoskeletal pain; early-onset osteoarthritis.
    • Other: Scoliosis; soft, velvety, hyperextensible skin; tissue fragility (e.g., easy bruising, poor wound healing).

Systemic Syndromes - Skeletal Footprints

• Down Syndrome (Trisomy 21):

  • Generalized hypotonia & ligamentous laxity → pes planus, patellar instability, hip instability/dysplasia.
  • Atlantoaxial Instability (AAI):
    • Screen: Powers ratio, Atlanto-Dental Interval (ADI) > 4-5 mm.
    • Surgical fusion if symptomatic or ADI > 10 mm.
  • Scoliosis common.

• Mucopolysaccharidoses (MPS): (Lysosomal GAG accumulation)

  • Dysostosis multiplex: oar-shaped ribs, bullet-shaped phalanges, anterior vertebral beaking.
  • Joint stiffness/contractures (cf. laxity in Down Syndrome).
  • Kyphosis (gibbus deformity), hip dysplasia, carpal tunnel syndrome.
  • Key Types:
    • Hurler (MPS I): severe, early onset, corneal clouding.
    • Morquio (MPS IV): severe skeletal dysplasia, AAI, normal intellect. 📌 Morquio: More Orthopedic, Rest (intellect) Quite Intact Often.

⭐ > In Down Syndrome, symptomatic Atlantoaxial Instability (AAI) or an ADI > 10 mm (even if asymptomatic) are indications for surgical stabilization.

Comparative Orthopedic Features:

High‑Yield Points - ⚡ Biggest Takeaways

• Osteogenesis Imperfecta: Blue sclera, recurrent fractures, hearing loss; COL1A1/A2 (Type I collagen) defects.
• Marfan Syndrome: Tall stature, arachnodactyly, upward lens subluxation, scoliosis; FBN1 defect; aortic root risk.
• Achondroplasia: Commonest dwarfism (FGFR3); rhizomelic shortening, trident hand, genu varum, spinal stenosis.
• Down Syndrome: Key risks: atlantoaxial instability, hip dysplasia, scoliosis, generalized ligamentous laxity.
• Neurofibromatosis Type 1: Café-au-lait spots, Lisch nodules, dystrophic scoliosis, tibial pseudoarthrosis.
• Mucopolysaccharidoses: Dysostosis multiplex, joint contractures, short stature, carpal tunnel syndrome.