SM 245a - Inherited Disorders of Connective Tissue Flashcards
Which connective tissue abnormality?
Mutationin COL1A1 or COL1A2
Osteogenesis imperfecta
(Abnormal Type I Collagen, due to COL1A1 or COL1A2 mutation; Autosomal dominant)
Which connective tissue abnormality?
Joint hypermobility
Ehlers-danos syndrome
(Abnormal Type V Collagen; COL5A1 or COL5A2; Autosomal dominant)
Which connective tissue abnormality?
Long limbs, fingers, toes
Marfan Syndrome
(Abnormal Fibrillin 1 -> impaired elastin function; autosomal dominant)
Which connective tissue abnormality?
Mutation in COL5A1
Ehlers-danos syndrome
(Abnormal Type V Collagen; COL5A1 or COL5A2; Autosomal dominant)
What gene mutation results in hypochondroplasia?
What is the result?
Mutation in FGFR3 (usually Gly380Arg)
- -> FGFR3 receptor is constituitively activated
- -> Constant inhibiton of chondrocyte hypertrophy
- Results in decreased chondrocyte proliferation, and therefore decreased bone growth
Describe the features of Ehlers-Danlos Syndrome
- Soft, velvety, hyperelastic, fragile skin
- Tears and bruises easily
- “cigarette paper” scars
- Molluscoid pseudotumors
- Joint hypermobility, dislocations
- Mitral valve prolpse
- Hiatal hernia
- Anal prolapse
What causes Ehlers-Danlos syndreome?
Abnormal Type V Collagen due to haploinsufficiency
Due to mutations in COL5A1 or COL5A2
Autosomal dominant
(Abnormal Type V Collagen; COL5A1 or COL5A2; Autosomal dominant)
Describe the features of perinatal lethal osteogenesis imperfecta
- Congenital fractures
- Accordion-like ribs: Chest wall is unstable, cannot inflate lungs
- Poor skull ossification “Wormian bones”
Which connective tissue abnormality?
Associated with mitral valve prolapse
Ehlers-danos syndrome
(Abnormal Type V Collagen; COL5A1 or COL5A2; Autosomal dominant)
Marfan Syndrome
(Fibrillin 1, Autosomal dominant)
What is the inheritance pattern of osteogenesis imperfecta?
Autosomal dominant
Varying forms
- Dominant negative = very severe
- Haploinsufficiency = mild
Describe the inheritance of Marfan Syndrome
Autosomal dominant
30% of cases are new mutations
Variable expressivity, fully penetrant
Which zone is affected by achondroplasia?
Zone of hypertrophy – it is too small
Chondrocyte hypertrophy, and therefore proliferation, is inhibited
(Contituitive inhibition due to FGFR3 mutation)
What causes osteogenesis imperfecta?
Abnormal Type I Collagen
Due to mutation in COL1A1 or COL1A2
Which connective tissue abnormality?
Hyperelastic, fragile skin
Ehlers-danos syndrome
(Abnormal Type V Collagen; COL5A1 or COL5A2; Autosomal dominant)
Describe the features of osteogenesis imperfecta
- Abnormal Type I collagen
- Wide range of severity
- Fractures with minimal trauma
- Tend to decrease after puberty
- Short limb dwarfism
- Blue sclera
Which connective tissue abnormality?
Fragile bones
Osteogenesis imperfecta
(Abnormal Type I Collagen, due to COL1A1 or COL1A2 mutation; Autosomal dominant)
What is the role of TGF-beta in the pathogenesis of Marfan syndrome?
Normally, fibrillin 1 forms a scaffold for the latent complex of TGF-beta
Abnormal fibrillin 1 (Marfan syndrome) means that the latent complex cannot bind, resulting in release of TGF-beta and excess TGF-beta signaling
- Emphysema
- Mitral valve prolapse
- Aortic aneurysm
- Also due to no fibrillin 1 scaffold for elastin
- Myopathy
Describe the features of Marfan syndrome
- Long limbs
- Long fingers and toes (thumb sign, wrist sign)
- Flat feet
- Scoliosis
- Ectopia Lentis
- Dislocation of the lens of the eye
- CV effects
- Aortic insufficiency, dilation, dissection
- Abdominal aortic aneurysm
- Pulmonary
- Pneumothorax
- Apical bleb
- Skin and integument
- Hernias
- Striae distensae
- CNS
- Dural ectasia
- Lumbosacra meningocele
Describe the pathophysiology of Marfan syndrome
Abnormal Fibrillin 1
- Monomers cannot associate to form connective tissue microfibrils in the inter-cellular matrix
- They are supposed to act as scaffolds for the deposition of tropoelastin in elastic fiber formation
- No scaffold ->
- Elastin function is disrupted
-
Latent complex released, TGF-beta activated; excess signaling
- Emphysema, mitral valve prolapse, aortic aneurysm, myopathy
Which connective tissue abnormality?
Wormian bones
Perinatal lethal osteogenesis imperfecta
(Abnormal Type I Collagen, due to COL1A1 or COL1A2 mutation; Autosomal dominant)
What is the potential role of NPR-B in treating achondroplasia?
- CNP activates NPR-B, resulting in the inhibition of the inhibitory pathway initiated by FGF:FGFR3
- This inhibits the inhibition of chondrocyte hypertrophy, resulting in the restored proliferation of chondrocytes
Which connective tissue abnormality?
Blue sclera
Osteogenesis imperfecta
(Abnormal Type I Collagen, due to COL1A1 or COL1A2 mutation; Autosomal dominant)
Which connective tissue abnormality?
Associated with aortic dilation, aortic regurgitation, aortic dissection, abdominal aortic aneurysm
Marfan Syndrome
(Abnormal Fibrillin 1 -> impaired elastin function; autosomal dominant)
Describe the radiographic findings of achondroplasia
- Roof of acetabulum is horizontal
- Ilium is a “paddle without a handle”
- Deep sacro-sciatic notch
