Bone Diseases

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Bone Diseases

• Dr Derakhshandeh, PhD

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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)
• Dominant
• or semi-dominant phenotype

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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

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Fibrillin gene
Marfan syndrome
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Osteogenesis imperfecta
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Osteogenesis imperfecta
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Definition

• Osteogenesis imperfecta
• a congenital (present from birth) condition of
  abnormal fragility of the bones

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CollagenFibrillin in EM
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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

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Collagens

• the fibrous protein constituent
• Insoluble
• extracellular glycoprotein
• found in all animals
• the most abundant proteins in the human body

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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

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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

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Tertiary Structure
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Extracellular processes of collagen synthesis
Prockop Kivirikko (1984)
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Genetic

• OI, TYPE IOSTEOGENESIS 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

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Osteogenesis imperfecta type I

• 110 000
• dominantly inherited (AD)
• Connective tissue disorder
• characterized mainly by bone
• fragility
• blue sclera
• 'functional null' alleles of COL1A1 on chromosome
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• or COL1A2 on chromosome 7
• lead to reduced amounts of normal collagen I

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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

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Glycine Serin
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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

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Arthrochalasia
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• 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

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OI Type I

• Osteogenesis imperfecta is the most common
  disorder
• Mutations inactivate one of the two copies of
  the COL1A1/2 gene

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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

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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

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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

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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

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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

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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

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OI

• Position effect (5/3- Mutation)
• Protein effect (Gly)
• Chain effect (aI/aII)

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Where is the COL1A1 gene located?

• Cytogenetic Location 17q21.3-q22.1
• Molecular Location on chromosome 17

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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

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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

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• CLINICAL FEATURES
• OI

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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

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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

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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

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EYES

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

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CARDIOVASCULAR

• Mitral valve prolapse occurred in 18 (3 times
  the prevalence in unaffected relatives)

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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)

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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

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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

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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

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Prevention

• Genetic counseling
• is recommended for prospective parents if one or
  both are affected by this disorder

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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

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Symptoms

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

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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)

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SKIN

• Skin elasticity
• OI type I increased elasticity in comparison to
  the type III patients

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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

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• CLINICAL FEATURES
• OII

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• OSTEOGENESIS IMPERFECTA CONGENITA,
• NEONATAL LETHAL FORMOSTEOGENESIS IMPERFECTA,
  TYPE IIOI
• Gene map locus 17q21.31-q22, 7q22.1

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OSTEOGENESIS IMPERFECTA, TYPE II
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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

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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

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• CLINICAL FEATURES
• OIII

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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

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TYPE III OI
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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.

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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

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• CLINICAL FEATURES
• OI IV

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OSTEOGENESIS IMPERFECTA, TYPE IV

• OI, TYPE IVOSTEOGENESIS IMPERFECTA WITH NORMAL
  SCLERAE
• Gene map locus 17q21.31-q22

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OSTEOGENESIS IMPERFECTA, TYPE IV
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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)

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Hypothesis

• Short stature
• tooth abnormalities
• low nasal bridge
• easy bruising
• bowed legs

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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.

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• Osteomyelitis

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Osteomyelitis

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

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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

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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.

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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

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Symptoms

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

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• Achondroplasia

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Achondroplasia

• Definition
• An inherited disorder of bone growth
• that causes the most common type of dwarfism

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Achondroplasia

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

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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

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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

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• 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

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Family with compound heterozygosity for N540K and
G380R mutations
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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

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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)

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• kyphosis and lordosis

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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