Bone Bone DiseasesDiseases

Dr Derakhshandeh, Dr Derakhshandeh, PhDPhD

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Dominant negative Dominant negative mutationsmutations

Dominant negative mutations:Dominant negative mutations:antimorphic mutationsantimorphic mutations an altered gene product that acts an altered gene product that acts

antagonistically to the wild-type alleleantagonistically to the wild-type alleleThese mutations usually result in an These mutations usually result in an

altered molecular functionaltered molecular function (often inactive):(often inactive):DominantDominantor semi-dominant phenotypeor semi-dominant phenotype

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Dominant negative Dominant negative mutationsmutationsIn 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 geneFibrillin geneMarfan syndrome

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Osteogenesis Osteogenesis imperfectaimperfecta

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Osteogenesis Osteogenesis imperfectaimperfecta

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DefinitionDefinition

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:

dermisTendonCartilageand 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:

Insolubleextracellular 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: boneand 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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GeneticGenetic 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

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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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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 substitutionsin 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 collagensuch 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 IVmissing pieces of the COL1A1/2 geneor 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

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CLINICAL FEATURESCLINICAL 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 FEATURESCLINICAL 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 FEATURESOI

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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 familiesbeginning 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 initiallybut often develops the classic 'cod-fish' appearance

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EYESEYES 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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EYESEYES

Hartikka et al. (2004) found that:

patients with COL1A1 mutations more frequently had blue sclerae than those with COL1A2 mutations

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CARDIOVASCULARCARDIOVASCULARMitral valve prolapse occurred in 18% (3 times the prevalence in unaffected relatives)

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EARSEARS 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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EARSEARS 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 Causes, incidence, and risk factorsfactors

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 Causes, incidence, and risk factorsfactors

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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PreventionPrevention

Genetic counseling: is recommended for

prospective parents if one or both are affected by this disorder

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SymptomsSymptoms 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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SymptomsSymptoms

• 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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SymptomsSymptoms• 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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SKINSKIN Skin elasticity OI type I increased elasticity

in comparison to the type III patients

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INHERITANCEINHERITANCE 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 FEATURESOII

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OSTEOGENESIS IMPERFECTA OSTEOGENESIS IMPERFECTA CONGENITA,CONGENITA,

NEONATAL LETHAL FORMNEONATAL LETHAL FORMOSTEOGENESIS IMPERFECTA, OSTEOGENESIS IMPERFECTA, TYPE IITYPE IIOIOI

Gene map locus Gene map locus 17q21.31-q22, 7q22.1

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OSTEOGENESIS IMPERFECTA, OSTEOGENESIS IMPERFECTA, TYPE IITYPE 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 brokenand multiple fractures can occur even

before birthThe chest is narrow with short ribs and underdeveloped

lungs

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Osteogenesis imperfecta, type IIAffected 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 FEATURESOIII

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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 TherapyGene 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 FEATURESOI 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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HypothesisHypothesismore 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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HypothesisHypothesisShort 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 4glycine 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