1. Bone Diseases
Dr Derakhshandeh, PhD

2. Dominant negative mutations
antimorphic mutations
an altered gene product that acts antagonistically to the wild-type allele
These mutations usually result in an altered molecular function
(often inactive):
Dominant
or semi-dominant phenotype

3. Dominant negative mutations
In humans:
Marfan syndrome is an example of a dominant negative mutation
occurring in an autosomal dominant disease
the defective glycoprotein product of the fibrillin gene (FBN1):
antagonizes the product of the normal allele

4. Marfan syndrome
Fibrillin gene

5. Osteogenesis imperfecta

6. Osteogenesis imperfecta

7. Definition Osteogenesis imperfecta:
a congenital (present from birth) condition of abnormal fragility of the bones

8. Collagen Fibrillin in EM

9. Collagen in most tissues and organs is most plentiful in: dermis
Tendon
Cartilage
and bone
as a scaffolding for our bodies
Controls cell shape
broken bones regenerate
and wounds heal

10. Collagens the fibrous protein constituent: Insoluble
extracellular glycoprotein
found in all animals
the most abundant proteins in the human body

11. Primary Structure of Collagens
The basic unit of collagens:
a polypeptide consisting of the repeating sequence
(Glycine (Gly) - X - Y)n
X is often Proline (Pro)
and Y is often hydroxyproline

12. Procollagen Type I The most common form of fibrillar collagen
It is a major constituent of:
bone
and skin
consists of a heterotrimer of:
two alpha1(I)
and one alpha2(I) chains

13. Tertiary Structure

14. Extracellular processes of collagen synthesis
Prockop & Kivirikko (1984)

15. Genetic OI, TYPE I OSTEOGENESIS IMPERFECTA WITH BLUE SCLERA
Gene map locus 17q21.31-q22, 7q22.1
OI type I phenotype can be produced by mutation in either the COL1A1 gene or the COL1A2 gene

16. Osteogenesis imperfecta type I
1:10 000
dominantly inherited (AD)
Connective tissue disorder
characterized mainly by bone
fragility
blue sclera
'functional null' alleles of COL1A1 on chromosome 17
or COL1A2 on chromosome 7
lead to reduced amounts of normal collagen I

17. What is the official name of the COL1A1 gene?
The official name of this gene is:
“collagen, type I, alpha 1”
COL1A1 is the gene's official symbol

23. Glycine Serin

24. What conditions are related to the COL1A1 gene?
Ehles-Donlos syndrome (AD)
Arthrochalasia:
(Short stature, Hyper elasticity of skin, AR, Problem with healing, N-Terminal defect
caused by mutations in the COL1A1/2 gene

25. Arthrochalasia

26. The mutations in the COL1A1/2 gene
instruct the cell to leave out a part of the pro-alpha1(I) chain that contains a segment used to attach one molecule to another
When this part of the protein is missing, the structure of type I collagen is compromised
Tissues that are rich in type I collagen:
such as the skin, bones, and tendons, are affected by this change

27. OI Type I Osteogenesis imperfecta is the most common disorder
Mutations: inactivate one of the two copies of the COL1A1/2 gene:

28. OI Type I
The mutated copy of the gene does not produce any pro-alpha1/2(I) collagen chains
Because only one copy of the gene:
cells from people with this disorder make only half of the normal amount of type I collagen:
which results in bone fragility and other symptoms

29. OI Type II
- caused by mutations in the COL1A1/2 gene
Many different types of mutations in the COL1A1/2 gene: can cause osteogenesis imperfecta type II
These mutations range:
from missing pieces of the COL2A1/2 gene
to amino acid substitutions
in which the amino acid glycine is replaced by another amino acid in the protein strand
C-terminal

30. OI Type II
Sometimes one end of the gene (called the C-terminus) is altered
which interferes with the association of the protein strands
All of these changes prevent the normal production of mature type I collagen
which results in this severe condition, type II osteogenesis imperfecta

31. OI Type III caused by mutations in the COL1A1/2 gene
Mutations in the COL1A1/2 gene may result:
unusable for collagen production
Other mutations cause the amino acid glycine to be replaced by a different amino acid in the pro-alpha1(I) chain
inhibits the essential interaction between protein chains

32. type III osteogenesis imperfecta
inability of the altered procollagen strands
These alterations negatively affect tissues that are rich in type I collagen
such as the skin, bones, teeth (Dentinogenesis imperfecta), and tendons

33. OI Type (IV) caused by mutations in the COL1A1/2 gene
Several different types of mutations in the COL1A1/2 gene cause osteogenesis imperfecta type IV
missing pieces of the COL1A1/2 gene
or changes in base pairs
formation of the mature triple-stranded collagen molecule

34. OI Position effect (5’/3’- Mutation) Protein effect (Gly)
Chain effect (aI/aII)

35. Where is the COL1A1 gene located?
Cytogenetic Location: 17q21.3-q22.1
Molecular Location on chromosome 17

36. CLINICAL FEATURES
Osteogenesis imperfecta:
Characterized chiefly by multiple bone fractures, usually resulting from minimal trauma
Affected individuals have blue sclerae, normal-near normal teeth, and normal or near-normal stature

37. CLINICAL FEATURES Osteogenesis imperfecta:
Fractures are rare in the neonatal period;
fracture tendency is constant from childhood to puberty
Often increases following menopause in women and after the sixth decade in men

38. CLINICAL FEATURES OI

39. CLINICAL FEATURES Fractures:
heal rapidly with evidence of a callus formation
and, with good orthopedic care, without deformity
Hearing loss;
occurs in about 50% of families
beginning in the late teens
to profound deafness, by the end of the fourth to fifth decade

40. CLINICAL FEATURES Radiologically: wormian bones are common
but bone morphology is generally normal at birth
Vertebral body morphology:
in the adult is normal initially
but often develops the classic 'cod-fish' appearance

41. EYES
Individuals with OI type I have distinctly blue sclera which remain intensely blue throughout life
The intensity of the blue fades with time: that these individuals may have sclerae of normal hue by adult life

42. EYES Hartikka et al. (2004) found that:
patients with COL1A1 mutations more frequently had blue sclerae than those with COL1A2 mutations

43. CARDIOVASCULAR
Mitral valve prolapse occurred in 18% (3 times the prevalence in unaffected relatives)

44. EARS In likely heterogeneous groups of patients with OI:
about half of affected individuals have hearing loss
that begins during the second decade as a conductive loss
Audiometry showed hearing loss in 25 patients (59.5%)

45. EARS
Hartikka et al. (2004) reported:
No correlation was found between the mutated gene or mutation type and hearing pattern
The authors interpreted this to mean that the basis of hearing loss in OI is complex
and that it is a result of multifactorial

46. Causes, incidence, and risk factors
All four types of OI are caused by defects in the amount or
structure of Type 1 collagen
an important part of the bone matrix

47. Causes, incidence, and risk factors
The defect may be inherited in an autosomal dominant pattern from an affected parent
This means that an affected parent, who carries a single gene for the disorder
has a 50% chance of having children with the disorder
Any child who inherits this gene will be affected

48. Prevention Genetic counseling:
is recommended for prospective parents if one or both are affected by this disorder

49. Symptoms OI: all of the bones are abnormally weak
The severity of the abnormality varies enormously from Type II OI
which is usually lethal in infancy (or even before birth)
Type I OI, which may be so mild that the diagnosis is not made, even in adulthood

50. Symptoms The three classic symptoms of OI includes: fragile bones
early hearing loss
and whites of the eyes that appear bluish (blue sclerae)

51. Symptoms not all people with OI will have blue sclerae or hearing loss
All do have fragile bones, but not all people with OI actually ever break a bone
penetrance of hearing loss is clearly age-dependent (Garretsen and Cremers, 1991)

52. SKIN
Skin elasticity
OI type I increased elasticity in comparison to the type III patients

53. INHERITANCE Paternal age effect:
for increased risk of new mutations has been documented
although it appears to be considerably lower than, for example, in Achondroplasia
Blumsohn et al. (2001) confirmed the presence of a small paternal age effect in apparently sporadic OI

54. CLINICAL FEATURES
OII

55. OSTEOGENESIS IMPERFECTA CONGENITA,
NEONATAL LETHAL FORM OSTEOGENESIS IMPERFECTA, TYPE II OI
Gene map locus 17q21.31-q22, 7q22.1

56. OSTEOGENESIS IMPERFECTA, TYPE II

57. Osteogenesis imperfecta, type II:
the most severe form of the disorder
Infants with the disorder:
have soft, fragile bones that may appear bent or crumpled
Bones are easily broken
and multiple fractures can occur even before birth
The chest is narrow
with short ribs and underdeveloped lungs

58. Osteogenesis imperfecta, type II
Affected infants:
have short bowed arms and legs; and unusually soft skull bones
Characteristic facial features include a small, narrow nose and a dark blue tint to the part of the eyeball that is usually white
Most infants with this condition are stillborn or die shortly after birth, usually from respiratory problems. A few children have lived from several months to a few years

59. CLINICAL FEATURES
OIII

60. OSTEOGENESIS IMPERFECTA, TYPE IIIOI
Gene map locus 17q21.31-q22, 7q22.1
The causative mutation in most cases lies in one of the genes for type I collagen, COL1A1 or COL1A2

61. TYPE III OI

62. TYPE III OI People with the disorder are much shorter than average
because the condition prevents bones from growing normally.
Spinal curvature (scoliosis)
and bone abnormalities often become progressively worse during childhood
but tend to stabilize during adolescence
These complications may shorten a person's lifespan by affecting heart and lung function
Other signs and symptoms include a light blue tint to the part of the eyeball that is usually white , brittle and discolored teeth, loose joints, and, in some cases, hearing loss.

63. Gene Therapy Chamberlain et al. (2004)
used adeno-associated virus vectors
to disrupt mutant COL1A1 collagen genes
in mesenchymal stem cells, from individuals with severe OI
demonstrating successful gene targeting in adult human stem cells

64. CLINICAL FEATURES
OI IV

65. OSTEOGENESIS IMPERFECTA, TYPE IV
OI, TYPE IV OSTEOGENESIS IMPERFECTA WITH NORMAL SCLERAE
Gene map locus 17q21.31-q22

66. OSTEOGENESIS IMPERFECTA, TYPE IV

67. Hypothesis
more than one broken bone occurring in a single episode (multiple)
present at birth
occuring after only minor trauma
a minority of people with OI never break a bone
deformed or short extremities (such as leg deformities or arm deformities)
deafness (conductive hearing loss may occur in adults)

68. Hypothesis Short stature tooth abnormalities low nasal bridge
easy bruising
bowed legs

69. Signs and tests
A physical examination may confirm the presence of fractures, deformities, and other symptoms.
Bone X-rays may show multiple healed fractures.
Once the specific molecular diagnosis is known, family members can be tested by a DNA blood test.
DNA testing on prenatal chorionic villus samples (CVS) can make the diagnosis during pregnancy.
Severe OI is visible on prenatal ultrasound as early as 16 weeks.

70. Osteomyelitis

71. Osteomyelitis Procedure
Osteomyelitis is an acute or chronic bone infection, usually caused by bacteria or by fungus

72. Causes, incidence, and risk factors Osteomyelitis
The infection that causes osteomyelitis:
often is in another part of the body and spreads to the bone via the blood
Affected bone may have been predisposed to infection because of recent trauma
In children:
the long bones are usually affected
In adults:
the vertebrae and the pelvis (hip) are most commonly

73. Osteomyelitis
Risk factors are recent trauma, diabetes, hemodialysis, and intravenous drug abuse. People who have had their spleen removed are also at higher risk for osteomyelitis
The incidence of osteomyelitis is 2 in 10,000 people.

74. Prevention Prompt and complete treatment of infections is helpful
High-risk people should see a health care provider promptly if they have signs of an infection anywhere in the body

75. Symptoms Pain in the bone Local swelling redness and warmth Fever
General discomfort, uneasiness, or ill feeling

76. Achondroplasia

77. Achondroplasia Definition An inherited disorder of bone growth
that causes the most common type of dwarfism

78. Achondroplasia its characteristic normal to large-sized head
shortened arms and legs (especially the upper arm)
a normal-sized trunk
and waddling gait

79. Achondroplasia Achondroplasia is inherited as an (AD) trait
However, the majority of cases, approximately 80%, appear as spontaneous mutations
If one parent has Achondroplasia, the infant has a 50% chance of inheriting the disorder
If both parents have the condition, the infant's chances of being affected increase to 75%

80. Genetics of Achondroplasia
99% of the affected individuals:
a single point mutation
in the Fibroblast Growth Factor Receptor gene3 (FGFR 3)
located on chromosome 4
glycine is substituted for arginine at codon 380 of FGFR 3

81. Such a mutation results:
in an abnormal cartilage and fibrous connecting tissue formation
Therefore, not only bones, but the ligaments, tendons and muscles of the patient with Achondroplasia are affected

82. Family with compound heterozygosity for N540K and G380R mutations

83. Prevention Genetic counseling may be helpful for prospective parents:
when one or both have achondroplasia
Because achondroplasia arises as a spontaneous mutation:
absolute prevention is not possible

84. Symptoms Short stature short limbs large appearing head
at birth:
Short stature
short limbs
large appearing head
Skeletal (limb) abnormality
Abnormal hand appearance
with persistent space between the long and ring fingers
marked kyphosis and lordosis (spine curvatures)

85. kyphosis and lordosis

86. Symptoms Waddling gait prominent forehead (frontal bossing)
increased inward curve of lower back
increased outward curve of upper back making back appear slightly hunched (kyphosis)
head appears disproportionately large for body
bowed legs