Transcript Osteogenesis imperfecta, type II

Bone Diseases
Dr Derakhshandeh, PhD
Marfan syndrome
2
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
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 imperfect
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
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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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Procollagen
Troprocollagen
Collagens
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Tertiary Structure
15
Extracellular processes of collagen
synthesis
Prockop & Kivirikko (1984)
16
 OI,
Genetic
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
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
18
Severity of disease
 Osteogenesis

imperfecta:
type II> type III> type IV> type I
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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

20
21
22
23
24
Glycine
Serin
25
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
26
Arthrochalasia
27
–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
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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 proalpha1/2(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 COL1A1/2
gene
 to amino acid substitutions
 in which the amino acid glycine is
replaced by another amino acid in the
protein strand
31
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
32
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
33
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 nearnormal stature
38
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
40
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
42
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)
45
 In
EARS
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
47
SKIN
 Skin
elasticity
 OI type I increased elasticity
in comparison to the type III
patients
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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
49
Prevention
 Genetic
counseling:
 is recommended for prospective
parents if one or both are
affected by this disorder
50
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
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)
•
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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 FORM
OSTEOGENESIS IMPERFECTA,
TYPE II
OI

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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CLINICAL
FEATURES
OIII
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OSTEOGENESIS IMPERFECTA,
TYPE III
 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 IV
OSTEOGENESIS IMPERFECTA WITH
NORMAL SCLERAE
 Gene map locus 17q21.31-q22

64
OSTEOGENESIS
IMPERFECTA, TYPE IV
65
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)
66
Hypothesis
 Short
stature
 tooth abnormalities
 low nasal bridge
 easy bruising
 bowed legs
67
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

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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
70
Achondroplasia
its characteristic normal to largesized 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
73
Family with compound heterozygosity
for N540K and G380R mutations
74
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
75
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

78