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MBOD Week 16 > Osteogenesis Imperfecta TBL > Flashcards

Osteogenesis Imperfecta TBL Flashcards

1
Q

Osteogenesis Imperfecta Type I

  • Severity
  • Symptoms: Skeletal, Eyes, Hearing, Teeth
A

Severity:
Mild (most common)

Symptoms:
Skeletal 
1. Recurrent Fracts. (dec. at puberty) 
2. ∆ Face 
3. Normal Height

Eyes
- Blue Sclerae

Hearing
- Presenile Deafness

Teeth: N/A

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2
Q

Osteogenesis Imperfecta Type II

  • Severity
  • Symptoms
A

Severity:
- Most Severe (prenatal/lethal)

Symptoms:
Skeletal
1. IN utero fractures 
2. Bowed bones/deformities
3. Small Chest (due to rib fracts)

Eyes:
- DARK Blue Sclerae

Teeth and Hearing: N/A

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3
Q

Osteogenesis Imperfecta Type III

  • Severity
  • Symptoms
A 
Severity: 
Moderately Severe (progressively deforming) 
Symptoms
Skeletal
1. Recurrent Fractures
2. Bony Deformities 
3. Short stature

Eyes
- Blue Sclera

Hearing
- Presenile Deafness

Teeth
- Dentinogenesis imperfecta

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4
Q

Osteogenesis Imperfecta Type IV

  • Severity
  • Symptoms
A

Severity:
Mild/moderate

Symptoms: 
Skeletal
- multiple recurrent fracts. 
- Bone Deformities (MORE than Type I) 
- Short Stature

Eyes
- normal or nearly normal sclerae

Hearing
- Presenile Deafness

Teeth
- Dentinogenesis Imperfecta

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5
Q

Osteogenesis Imperfecta Type VIII

  • Severity
  • Symptoms
A

Severity:
- Lethal congenital

Symptoms:
same as type II
Skeletal
1. IN utero fractures 
2. Bowed bones/deformities
3. Small Chest (due to rib fracts)

Eyes:
- NORMAL scelera

Teeth and Hearing: N/A

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6
Q

What is the only type of OI that is autosomal recessive?

A

Type VIII

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7
Q

What types of OI are familial?

- why is this important?

A

Type I and IV

*If genetic its AUTOSOMAL dominant, and there is a 1/2 chance of having an affected child

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8
Q

Explain Autosomal Dominant new mutations.

A
  • No family history of the disease

- ONLY one bad allele leads to disease (AD)

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9
Q

What are the recurrence risks for a family with a child who has and AUTOSOMAL DOMINANT version of OI that has come about from a new mutation?

A
  • Low, because its a spontaneous mutation
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10
Q

What risk does a child with AutoDom OI that arose from a new mutation have of passing the same disease to their kids?

A

50% - typically the risk is less than this because of reduced fertility in affected people

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11
Q

What may be the case for a family that has no history of OI, but has multiple Children with OI?

A

Germline Mosaicism

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12
Q

How does germline mosaicism manifest?

A

Early in embryonic Development a mutation happens in the cells that will become germ cells

  • this means only germ and no somatic cell are affected
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13
Q

T or F: Cardiovascular issues as well as motor delays are sometimes associated with OI

A

True

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14
Q

T or F: miscarriages are frequent with severe types of OI

A

True

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15
Q

What causes shortened stature of patients with OI?

A
  • Compression Fractures in Vertebrae

Codfish Vertebrae

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16
Q

Where do most OI fractures occur?

A

Long Bones > Ribs/Skull

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17
Q

What two genes are responsible for making strands used in type I Collagen?
- Strand Type?

A

COLA1 - pro-alpha1

COLA2 - pro-alpha2

18
Q

How many of each chain type are used to make type Collagen type I?

A

2 Pro-alpha1 chains

1 Pro-alpha2 chain

19
Q

What happens with a change in expression of pro-alpha1 or pro-alpha2?

A

Type 1 collagen will get messed up because RATIO will be off

20
Q

What is the chromosome location for the pro-alpha1 and pro-alpha2 gene?

A

Pro-alpha1 - Chrom. 17

Pro-alpha2 - Chrom. 7

21
Q

What is the incidence of OI?

A

1/10,000 births in every race

22
Q

What other diseases/issues could result in fractures early in childhood?

A
  1. Ehlers-Danlos - hypermobility causing inc. fracts.
  2. Child abuse
  3. osteoporosis
    - other genetic diseases
23
Q

What chromosome is most commonly mutated resulting in defective type I collagen?

A

Chromosome 17

24
Q

T or F: the are only a small number of mutations that lead to OI?

A

False, there is TONS of allelic heterogeneity in OI mutations, more than 200 described

25
Q

What are the two general categories of protein product that result from mutations?

A
  1. Decreased Production of normal Collagen

2. Abnormal Collagen Structure

26
Q

Which general category does OI type I fall into?

  • Decreased Production of Normal Collagen
  • Abnormal Collagen
A

*Decreased production of normal collagen

27
Q

What types of OI result from abnormal structure of type I collagen?

A

Types II, III, IV

28
Q

What are some of the causes of decreased type I collagen formation in Type I OI?

A
  1. Prematrue Termination codons
  2. decreased STABILITY of mRNA of proalpha1
  3. decreased AMOUNT of pro-alpha1

***Note: these decrease the amount of pro-alpha1 and lead to messed up ratios

29
Q

T or F: OI Type I is always the result of pro-alpha1 alterations

A

True

30
Q

T or F: OI types II-IV result from issues in EITHER pro-alpha1 or pro-alpha2

A

True

31
Q

What is the most frequent cause of OI types II-IV?

A

Substitution of another amino acid for glycine

32
Q

T or F: mutations at the N-terminal end of the triple helix are usually lethal?

A

False, C-terminal end mutations are usually lethal

33
Q

What can overmodification of collagen cause?

A
  • May slow Fibril formation causing OI type II-IV.
34
Q

What specific abnormality leads to type VIII OI?

- Collagen type affected

A
  • Altered 3-hydroxylation of a single proline on pro-alpha1

- Type I collagen affected

35
Q

What is the clinical significance of being able to differentiate between Type II OI and Type VIII OI?

A
  • Type VIII is autosomal recessive so their is a 1/4 recurrence risk which is higher than type II that often results from spontaneous mutation
36
Q

What is the earliest you could find out if your kid has OI?

A

10 weeks via CVS or Amniocentesis

37
Q

What is the Dominant negative affect?

A

Mutated Protein Product is not only defective but also is detrimental to the activity of the protein product from the normal allele

38
Q

Why would Collagen be particularly susceptible to the Dominant toxic affect?

A

The affect is usually seen on Multimeric proteins like Collagen

-one bad subunit screws up the entire protein

39
Q

Have a CVS has been performed what are the two testing options for OI?

A

Molecular - collagen analysis
**Note: Amniocentesis may also be performed for molecular

Biochemical analysis

40
Q

If a defect can be detected on fetal ultrasound, what does that suggest?

A
  • Suggests SEVERE OI

**Types I and IV would not be detected

41
Q

How do we usually treat OI?

A

Treat symptoms:

  • Limit activities
  • Use water beds
  • Use Braces etc.
42
Q

How would you differentiate OI III and IV from OI I?

A

Dentigenesis Imperfecta

MBOD Week 16 (4 decks)

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