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USMLE Biochemistry > Connective tissue disease > Flashcards

Connective tissue disease Flashcards

1
Q

What are the 3 key components of connective tissue?

A
  • Collagen
  • Elastin
  • Fibrillin
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2
Q

What is the basic structure of collagen?

A

Triple helix
- 3 long alpha chains

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3
Q

What specific amino acids are highly abundant in collagen?

A
  • Proline
  • Lysine
  • Glycine (mainly)
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4
Q

What disease has defective production of type 1 collagen?

A

Osteogenesis imperfecta

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5
Q

What tissues contain type 1 collagen?

A
  • Bone
  • Skin
  • Tendons, ligaments
  • Cornea
  • Internal organs
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6
Q

What tissues contain type 2 collagen?

A
  • Cartilage
  • Intervertebral discs
  • Vitreous humor (eye)
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7
Q

What tissues contain type 3 collagen?

A
  • Skin
  • Blood vessels
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8
Q

Collagen (type 1, 2, 3) molecules that assemble into polymers are known as what?

A

Fibrils

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9
Q

What tissues contain type 4 collagen?

A
  • Basement membrane
  • Basal lamina (beneath epithelial layer)
  • Lens
  • Cochlea
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10
Q

What is ALport’s syndrome?

A

X-linked recessive type 4 collagen defect
- Mutations to alpha-3,4,5 chains

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11
Q

What is the calssic triad of symptoms in Alport syndrome?

A

Male with:
- Hematuria
- Hearing loss
- Occular disturbances

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12
Q

Where are the alpha chains of collagen synthesized?

A

Rough ER
- Contains signal molecules
- Pre-procollagen

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13
Q

What are the alpha chains referred to once signal molecules are added and they enter to ER lumen?

A

Pro-alpha chains

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14
Q

What occurs in the Endoplasmic reticulum lumen to pro-alpha chains?

A
  • Proline and lysines hydroxylated
  • Hydroxylysines glycosylated (sugar added to hydroxylysine)
  • Propeptides (extra amino acids), disulfide bonds
  • 3 pro alpha chains combine -> procallagen
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15
Q

What does hydroxylation of proline and lysine require?

A

Vit C
- (Hydroxy)lysine or proline

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16
Q

What cannot form in vit c deficiency (scurvy)?

A

Defective pro-alpha chains
- Do not form triple helix

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17
Q

What are propeptides?

A

Extra amino acids added to N and C ends of pro-alpha chains

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18
Q

What do the 3 pro-alpha chains combine to form?

A

Procollagen

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19
Q

After propeptides (from N and C terminal) cleaved what is formed?

A

Tropocollagen

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20
Q

What are the extracellular modifications that occur to tropocollagen?

A

Collagen fibrils form - self assemble as less soluble
- Strenthened thru lysine crosslinking
-

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21
Q

What are collagen fibers?

A

Bundels of triple helixes

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22
Q

What extracellular enzyme crosslinks lysine to form collagen fibrils?

A

Lysyl oxidase

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23
Q

What does lysyl oxidase require as a cofactor?

A

Copper

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24
Q

What are wrinkles due to?

A
  • Decreased production of elastin and collagen in dermis
  • Collagen/elastin fibers also thicken and clump
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25
What is sclroderma caused by?
Fibroblast activation - Excess collagen deposition - Stiff hardened tissues (skin, organ systems)
26
What kind of disorder is scleroderma
Autoimmune
27
Mutation in what genes causes type 1 osteogenesis imperfecta?
COL1A1 or COL1A2 genes - Code for alpha chains for type 1 collagen
28
Rank the types of osteogenesis imperfecta in terms of severity?
II, III, IV, I - II is lethal in utero
29
What are the symptoms of osteogenesis imperfecta?
- Fractures with minimal trauma (beware of child abuse) - Blue sclera - Hearing loss (abnormal malleus, incus, stapes)
30
Dentinogenesis imperfecta (discoloured, translucent or shiny teeth), fall out easily) This condition is most commonly associated with what disease?
- Type III, IV osteogenesis imperfecta - Rarely type 1
31
What are ehlers danlos syndromes generally all due to?
Defective collagen synthesis
32
What genes cause classic Ehlers Danlos syndrome?
COL5A1 and COL5A2
33
How is ehlers danlos syndrome inherited?
Aut Dominant
34
What type of collagen is defective in Ehlers danlos syndrome?
Type V (interacts with other collagens)
35
What genes cause vascular Ehlers danlos syndrome?
COL3A1
36
What type of collagen is defective in vascular ehlers danlos syndrome?
Type 3
37
What are the clinical features of classic type (type V collagen) ehlers danlos syndrome?
- Hypermobile joints - Hyperextensible (velvity) skin - Easy bruising - Think wide 'cigarette paper' scars - Mitral valve prolapse
38
Ehlers danlos syndrome (vascular type, type 3 collagen) classically has what features?
- Thin skin, easy bruising - Aneurysms - berry - Intestinal perforation - Uterus rupture during pregnancy
39
What percentage of those with Ehlers danlos syndrome (vascular type, type 3 collagen) have a vascular event / rupture by 40?
80% - Median age of death is 48 years old
40
Menkes disease is inherited how?
X linked recessive
41
Menkes disease is a disease of what gene and what does it code for?
ATP7A - ATPase which uptakes/transports copper
42
Impaired copper absorption (Menkes disease) causes a deficiency in what enzyme?
Lysyl oxidase - Involved in collagen synthesis
43
Gene which causes Wilsons disease?
ATP7B
44
Clinical features of Menkes disease?
- Sparse, brittle (kinky) hair - Low body temp - Hypotonia, seizures - Poor growth - Developmental delay - Osteoperosis / fractures - Fatal usually in childhood
45
Elastin is found where?
Main component of elastic fibres (allows stretching/recoil) - Arteries (50% of aortic tissue) - Skin - Lungs - Ligaments - Vocal cords - Ligamentum flava
46
What amino acids are contained in elastin?
- Glycine - Lysine - Proline
47
Since elastin contains the same amino acids as collagen what differentiates it?
Most are non-hydroxylated - No hydroxylysine - Some hydroxyproline Also not glycosylated
48
what is elastin excreted as?
Tropoelastin (assembled into elastin fibers with crosslinking)
49
Alpha 1 antitrypsin inhibits what enzyme?
Elastase
50
Emphysema is caused by an inbalance between what?
Neutrophil elastase (destroys elastase) and elastase inhibitor (AAT) protects elastin - Incr elastase decr AAT
51
Williams syndrome is due to a chromosomal abnormality in what chr?
Partial deletion on long arm of chr 7
52
What protein is not present in Williams syndrome?
Elastin
53
What are the clinical features of Williams syndrome?
- Elfin appearence, IQ impaired - Supravalvular aortic stenosis (constriction of ascending aorta above aortic valve)
54
What is the major component of microfibrils?
Fibrillin
55
What kind of protein is fibrillin?
Glycoprotein
56
What are microfibrils?
Sheath that surrounds elastin core
57
What are elastic fibres composed of?
- Elastin - Microfibrils (made of fibrillin) - Other molecules
58
A deficiency in fibrillin (component of microfibrils) causes what syndrome?
Marfan
59
What gene causes Marfans? Where is it located?
FBN1 gene (codes for fibrillin-1) - Chr 15
60
What is the wrist and thumb sign? (Marfans)
Wrist sign - Tip of thumb covers entire fingernail of fifth finger Thumb sign - Thumb protrudes beyond ulnar border
61
What eye signs can be seen in Marfans?
- Cataracts (early age) - Dislocation of lens (commonly due to trauma) - Lens classically dislocated in upward/outward direction
62
What are the CV associations with Marfan?
Mitral valve prolapse Thoracic aortic aneurysm and dissection - Cystic medial necrosis - Cysts and necrosis pf medial layer
63
What other conditions may have a Marfinoid habitus?
- Homocystinuria - MEN 2B - Rare forms of Ehlers Danlos

USMLE Biochemistry (44 decks)

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