Transcript Document

SMA
SPINAL MUSCULAR
ATROPHY
Dr Pupak Derakhshandeh, PhD
Ass Prof of Medical Science of Tehran
University
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Mutation Detection &
PND
-Thalassemia/ -Thalassemia
• Haemophilia (A / B)
• HbD, G, E, S
• DMD/BMD
• SMA(I-III)
• CF; …
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DELETION OF SMN AND
NAIP GENES IN IRANIAN
PATIENTS WITH SPINAL
MUSCULAR ATROPHY
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SMA
Gene: SMN (Survival Motor Neuron)
Motor Neuron; Anterior Horn; Spinal
Cord
Second most common fatal autosomal
recessive disorder after CF
Second most common pediatric
neuromuscular disorder after DMD
Incidence : 1 in 6000-10000 live births
Carrier frequency : 1 in 40-60
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CLASSIFICATION
SMA TYPE I (Werdnig-Hoffmann)
SMA TYPE II (Classic)
SMA TYPE III (Kugelberg-Welander)
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SMA TYPE I
Severe form of SMA
Onset : first 6 months
Death : < 2 year
Never raising the head or sitting
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SMA TYPE II
Less sever
Clinical appearing : < 18 months
Able to sit unaid
Death : about 9 years
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SMA TYPE III
Mildest form of SMA
Onset : > 18 months
Walking without aid
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OTHER
CLASSIFICATION
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DIAGNOSIS
EMG
Muscle Biopsy
Genetic Testing/PND
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GENETICS
1990: The three types of SMA were
mapped to 5q13
The SMA locus contain two inverted
copies of a 500kb element
The two copies named telomeric and
centromeric
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GENETIC MAP
Three candidate genes named SMN
(Survival Motor Neuron), NAIP (Neuronal
Apoptosis Inhibitory Protein) and P44
were identified in this locus
Up to 95% of SMA patients (SMNI-III) are
homozygously deleted for two exons (7&8)
of both telomeric copy of SMN gene
(SMNt)
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Deletions
Up to 5% of SMA patients have
frameshift mutations, gene conversions
and point mutation
Exons 5 and 6 of NAIPt gene are
deleted in approximately 50% of type
I SMA and 18% of types II and III SMA
P44t is lacked or intrrupted in 73% of
SMA type I patients and 7% in types II
and III
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The summery of normal alleles (N) , mutant
alleles (M) and deletion types (D) of SMN
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MOLECULAR
DIAGNOSIS & PND
PCR-SSCP or PCR-RFLP of SMN
gene enables confirmation of a
suspected clinical diagnosis of SMA
or prenatal diagnosis
These two techniques based on
nucleotide differences of both exon 7
and exon 8 of telomeric and
centromeric copy of SMN
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Deletion Analysis of
SMN gene
Exones 7 and 8 of
SMN gene were
amplified and cut
by Dra I and Dde I ,
respectively. (only
centromeric copy
is cutted)
Absence of SMNt
exone(s) 7 (and 8)
confirm diagnosis
of SMA
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Exon 7, DraI
188 bp
164 bp
Exon 8, DdeI
188 bp
123 bp
65 bp
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SMN Deletion Analysis
SMNt Exon 7
is deleted in
affected child
Derakhshandeh-Peykar, et al. Annal Acad Med, 2007
(Depart Med Gen & NRCGEB)
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NAIP Gene Deletion
Analysis
Exones 5 & 6 of NAIP gene were amplified
with exon 13 which was the internal control
Absence of exon
5 and exon 6 ( which
only exist within the
telomeric functional
copy of NAIP) was
detected in ~50% of
type I SMA and 18%
of types II and III SMA
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NAIP Deletion analysis
Derakhshandeh-Peykar, et al. Annal Acad Med, 2007
(Depart Med Gen & NRCGEB)
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The objective of this study was to
genetically characterize the childhood onset
spinal muscular atrophy in Iran.
SMN
NAIP
Deletion of exon 7 & Deletion of exon 5 &
8
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SMA type I (n=70)
70(100%)
61(87%)
SMA type II (n=3)
2(66%)
1(33%)
SMA type III (n=2)
1(50%)
0(0%)
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Various deletion haplotypes were constructed by using
genotypes of SMN and NAIP genes.
Haplotype A, which has the deletions of all two involved genes,
were deleted in approximately 83% of type I and II SMA but not
in type III and was found predominantly in the severe group
with an early onset at less than 6 month of age.
we report Thirty four our experiences for prenatal diagnosis
Haplotypes (%)
A
B
C
SMA type I
(n=70)
87
100
0
SMA type II
(n=3)
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66
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SMA type III
(n=2)
0
50
50
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These studies suggested that the frequency
of gene deletions of SMN1 and NAIP gene
is a few higher than previous reports. It is
may be due to high rate of consanguine
marriage by Iranian Muslims (96 % in this
families). Thus, the conformation of SMA
related gene deletion will also be a useful
tool for the pre and postnatal diagnostic. In
addition to common PCR methods for SMN
exon 7 and 8 and NAIP exons 4 and 5, we
also conducted multiplex PCR of exon 5, 6
and 13 of the NAIP telomere in one
reaction.
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Derakhshandeh
Esmaiili
Rahmani
Babrzadeh
Taeb
Attaran
Sajedifar
Farhud
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