1. Bone Diseases Dr Derakhshandeh, PhD

2. 2 Marfan syndrome

3. 3 Dominant negative mutations Dominant negative mutations: 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): (often inactive): Dominant Dominant or semi-dominant phenotype or semi-dominant phenotype

4. 4 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

5. 5 Fibrillin gene Marfan syndrome

6. 6 Osteogenesis imperfecta

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8. 8 Definition Osteogenesis imperfecta: a congenital (present from birth) condition of abnormal fragility of the bones

9. 9 Collagen Fibrillin in EM

10. 10 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

11. 11 Collagens the fibrous protein constituent:  Insoluble  extracellular glycoprotein  found in all animals  the most abundant proteins in the human body

12. 12 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

13. 13 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

14. 14 Collagens Procollagen Troprocollagen

15. 15 Tertiary Structure

16. 16 Extracellular processes of collagen synthesis Prockop & Kivirikko (1984)

17. 17Genetic OI, TYPE I OSTEOGENESIS IMPERFECTA WITH BLUE SCLERA Gene map locus 17q21.31-q22, 7q22.117q21.31-q22, 7q22.1 OI type I phenotype can be produced by mutation in either the COL1A1 gene or the COL1A2 gene

18. 18 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

19. 19 Severity of disease Osteogenesis imperfecta:  type II> type III> type IV> type I

20. 20 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

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25. 25 Glycine Serin

26. 26 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 gene

27. 27 Arthrochalasia

28. 28 –The mutations in the COL1A1/2 gene –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

29. 29 OI Type I  Osteogenesis imperfecta is the most common disorder  Mutations: inactivate one of the two copies of the COL1A1/2 gene:

30. 30 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

31. 31 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 COL1A1/2 gene to amino acid substitutions in which the amino acid glycine is replaced by another amino acid in the protein strand

32. 32 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

33. 33 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

34. 34 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

35. 35 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

36. 36 OI Position effect (5’/3’- Mutation) Protein effect (Gly) Chain effect (aI/aII)

37. 37 Where is the COL1A1 gene located? Cytogenetic Location: 17q21.3-q22.1 Molecular Location on chromosome 17

38. 38 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

39. 39 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

40. 40 CLINICAL FEATURES OI

41. 41 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

42. 42 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

43. 43 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

44. 44 EYES Hartikka et al. (2004) found that: patients with COL1A1 mutations more frequently had blue sclerae than those with COL1A2 mutations

45. 45 CARDIOVASCULAR Mitral valve prolapse occurred in 18% (3 times the prevalence in unaffected relatives)

46. 46 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%)

47. 47EARS 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

48. 48 SKIN Skin elasticity OI type I increased elasticity in comparison to the type III patients

49. 49 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

50. 50 Prevention Genetic counseling: is recommended for prospective parents if one or both are affected by this disorder

51. 51 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

52. 52 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)

53. 53INHERITANCE 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. 54 CLINICAL FEATURES OII

55. 55 OSTEOGENESIS IMPERFECTA CONGENITA, OSTEOGENESIS IMPERFECTA CONGENITA, NEONATAL LETHAL FORM OSTEOGENESIS IMPERFECTA, TYPE II OI NEONATAL LETHAL FORM OSTEOGENESIS IMPERFECTA, TYPE II OI Gene map locus 17q21.31-q22, 7q22.1 Gene map locus 17q21.31-q22, 7q22.117q21.31-q22, 7q22.117q21.31-q22, 7q22.1

56. 56 OSTEOGENESIS IMPERFECTA, TYPE II

57. 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. 58 CLINICAL FEATURES OIII

59. 59 OSTEOGENESIS IMPERFECTA, TYPE III Gene map locus 17q21.31-q22, 7q22.117q21.31-q22, 7q22.1 The causative mutation in most cases lies in one of the genes for type I collagen, COL1A1 or COL1A2

60. 60 TYPE III OI

61. 61 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.

62. 62 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

63. 63 CLINICAL FEATURES OI IV

64. 64 OSTEOGENESIS IMPERFECTA, TYPE IV OI, TYPE IV OSTEOGENESIS IMPERFECTA WITH NORMAL SCLERAE Gene map locus 17q21.31-q2217q21.31-q22

65. 65 OSTEOGENESIS IMPERFECTA, TYPE IV

66. 66Hypothesis 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) deafnesshearing loss

67. 67 Hypothesis Short stature tooth abnormalities low nasal bridge easy bruising bowed legs

68. 68 Signs and tests A physical examination may confirm the presence of fractures, deformities, and other symptoms.physical examinationfractures Bone X-rays may show multiple healed fractures. Bone X-rays 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.

69. 69 Achondroplasia

70. 70 Achondroplasia Definition An inherited disorder of bone growth that causes the most common type of dwarfism

71. 71 Achondroplasia its characteristic normal to large- sized head shortened arms and legs (especially the upper arm) a normal-sized trunk and waddling gait

72. 72 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%

73. 73 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

74. 74 Family with compound heterozygosity for N540K and G380R mutations

75. 75 Prevention Genetic counseling may be helpful for prospective parents: Genetic counseling when one or both have Achondroplasia Because Achondroplasia arises as a spontaneous mutation:  absolute prevention is not possible

76. 76 Symptoms 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)

77. 77 kyphosiskyphosis and lordosislordosis

78. 78 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