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USMLE Biochemistry > Connective tissue disease > Flashcards

Connective tissue disease Flashcards

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USMLE® Step 1 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
Q

What is sclroderma caused by?

A

Fibroblast activation
- Excess collagen deposition
- Stiff hardened tissues (skin, organ systems)

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26
Q

What kind of disorder is scleroderma

A

Autoimmune

27
Q

Mutation in what genes causes type 1 osteogenesis imperfecta?

A

COL1A1 or COL1A2 genes
- Code for alpha chains for type 1 collagen

28
Q

Rank the types of osteogenesis imperfecta in terms of severity?

A

II, III, IV, I

  • II is lethal in utero
29
Q

What are the symptoms of osteogenesis imperfecta?

A
  • Fractures with minimal trauma (beware of child abuse)
  • Blue sclera
  • Hearing loss (abnormal malleus, incus, stapes)
30
Q

Dentinogenesis imperfecta (discoloured, translucent or shiny teeth), fall out easily)

This condition is most commonly associated with what disease?

A
  • Type III, IV osteogenesis imperfecta
  • Rarely type 1
31
Q

What are ehlers danlos syndromes generally all due to?

A

Defective collagen synthesis

32
Q

What genes cause classic Ehlers Danlos syndrome?

A

COL5A1 and COL5A2

33
Q

How is ehlers danlos syndrome inherited?

A

Aut Dominant

34
Q

What type of collagen is defective in Ehlers danlos syndrome?

A

Type V (interacts with other collagens)

35
Q

What genes cause vascular Ehlers danlos syndrome?

A

COL3A1

36
Q

What type of collagen is defective in vascular ehlers danlos syndrome?

A

Type 3

37
Q

What are the clinical features of classic type (type V collagen) ehlers danlos syndrome?

A
  • Hypermobile joints
  • Hyperextensible (velvity) skin
  • Easy bruising
  • Think wide ‘cigarette paper’ scars
  • Mitral valve prolapse
38
Q

Ehlers danlos syndrome (vascular type, type 3 collagen) classically has what features?

A
  • Thin skin, easy bruising
  • Aneurysms - berry
  • Intestinal perforation
  • Uterus rupture during pregnancy
39
Q

What percentage of those with Ehlers danlos syndrome (vascular type, type 3 collagen) have a vascular event / rupture by 40?

A

80%
- Median age of death is 48 years old

40
Q

Menkes disease is inherited how?

A

X linked recessive

41
Q

Menkes disease is a disease of what gene and what does it code for?

A

ATP7A
- ATPase which uptakes/transports copper

42
Q

Impaired copper absorption (Menkes disease) causes a deficiency in what enzyme?

A

Lysyl oxidase
- Involved in collagen synthesis

43
Q

Gene which causes Wilsons disease?

A

ATP7B

44
Q

Clinical features of Menkes disease?

A
  • Sparse, brittle (kinky) hair
  • Low body temp
  • Hypotonia, seizures
  • Poor growth
  • Developmental delay
  • Osteoperosis / fractures
  • Fatal usually in childhood
45
Q

Elastin is found where?

A

Main component of elastic fibres (allows stretching/recoil)
- Arteries (50% of aortic tissue)
- Skin
- Lungs
- Ligaments
- Vocal cords
- Ligamentum flava

46
Q

What amino acids are contained in elastin?

A
  • Glycine
  • Lysine
  • Proline
47
Q

Since elastin contains the same amino acids as collagen what differentiates it?

A

Most are non-hydroxylated
- No hydroxylysine
- Some hydroxyproline

Also not glycosylated

48
Q

what is elastin excreted as?

A

Tropoelastin (assembled into elastin fibers with crosslinking)

49
Q

Alpha 1 antitrypsin inhibits what enzyme?

A

Elastase

50
Q

Emphysema is caused by an inbalance between what?

A

Neutrophil elastase (destroys elastase) and elastase inhibitor (AAT) protects elastin

  • Incr elastase decr AAT
51
Q

Williams syndrome is due to a chromosomal abnormality in what chr?

A

Partial deletion on long arm of chr 7

52
Q

What protein is not present in Williams syndrome?

A

Elastin

53
Q

What are the clinical features of Williams syndrome?

A
  • Elfin appearence, IQ impaired
  • Supravalvular aortic stenosis (constriction of ascending aorta above aortic valve)
54
Q

What is the major component of microfibrils?

A

Fibrillin

55
Q

What kind of protein is fibrillin?

A

Glycoprotein

56
Q

What are microfibrils?

A

Sheath that surrounds elastin core

57
Q

What are elastic fibres composed of?

A
  • Elastin
  • Microfibrils (made of fibrillin)
  • Other molecules
58
Q

A deficiency in fibrillin (component of microfibrils) causes what syndrome?

A

Marfan

59
Q

What gene causes Marfans?
Where is it located?

A

FBN1 gene (codes for fibrillin-1)
- Chr 15

60
Q

What is the wrist and thumb sign? (Marfans)

A

Wrist sign
- Tip of thumb covers entire fingernail of fifth finger

Thumb sign
- Thumb protrudes beyond ulnar border

61
Q

What eye signs can be seen in Marfans?

A
  • Cataracts (early age)
  • Dislocation of lens (commonly due to trauma)
  • Lens classically dislocated in upward/outward direction
62
Q

What are the CV associations with Marfan?

A

Mitral valve prolapse

Thoracic aortic aneurysm and dissection
- Cystic medial necrosis
- Cysts and necrosis pf medial layer

63
Q

What other conditions may have a Marfinoid habitus?

A
  • Homocystinuria
  • MEN 2B
  • Rare forms of Ehlers Danlos

USMLE Biochemistry (44 decks)

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