Transcript PPT

The Molecular Basis of
Muscular Dystrophy
肌肉萎缩症的分子基础
AUTHER：刘少伟
刘寅
王青
吕潇
肌肉萎缩症
（假性肥大肌营养不良）
A Baby of seven month
Connective tissue结缔组织
What Are Muscular
Dystrophies?
The muscular dystrophies are a group of
Muscle diseases which have three features
in common:
• muscle-fiber degeneration and muscle
weakness
• Hereditary: It passes from parent to
child
• Progressive: It gets worse over time
Different Types of MD
There are nine major types of MD
affecting people of all ages, from
infancy（幼年）to middle age or later.
The two most common types of MD
affect children:
• Duchenne muscular dystrophy (DMD)
• Becker muscular dystrophy (BMD)
Guillaume Duchenne
• Guillaume Benjamin Amand
Duchenne is the man credited with
identifying the symptoms and
naming the disease known as
Duchenne Muscular Dystrophy.
• He was a medical doctor that
became very interested in the
relationship between electric
stimulation and muscles. This
interest caused him to travel from
hospital to hospital in an attempt
to experiment with and treat
those with muscular
diseases. Along his journey, he
encountered and recorded details
of many boys who had the
condition that he identified as
Duchenne Muscular Dystrophy.
Why are DMD and BMD
discussed together?
DMD and BMD cause similar patterns of
weakness and disability and are inherited in
the same way.
Because they are due to defects of the same
gene on the X chromosome which encodes a
protein —— “dystrophin”.
They are inherited as X-linked recessive
diseases.
( X染色体隐性基因 ）
The gene of Dystrophin
(抗肌肉萎缩蛋白)
The gene responsible for DMD and
BMD is named dystrophin。It’s the largest
gene so far identified in the mammalian(哺乳动
物)genome .
The gene stretches for more than 2.3
million bases along the X chromosome , a
length that requires 16 hours to be transcribed
into a single mRNA!
Only about 0.6 % of the gene actually codes
for amino acids(exons); the remaining 99.4%
consist of noncoding introns .
The exons are put
together for code
assembly during a
process called
splicing.
Due to its length
the Dystrophin gene
is relatively
vulnerable for
rearrangements
(mutations)
X-linked recessive diseases
The protein dystrophin reside in the
membrane skeleton of striatedmuscle(横纹肌)
cells.
It is important for the strength and
flexibility of the muscle fiber membranes.
Dystrophin are rod-shaped dimers
（杆状二聚物） beneath the plasma
membrane
laminin
DAP
(dystophin-associated
proteins)
dystrophin
F-actin
On their cytoplasmic side ,dystrophin molecules are
attached to actin filaments, and on their membrane side, they
are attached to a cluster of dystophin-associated proteins
(DAPs), in turn, are linked on their extracellular surface to
components of the basement membrane that surround these
contractile(有收缩性的) cells. Taken together, these various
proteins form a functional pathway linking the extracellular
matrix with the internal cytoskeleton. In addition, dystrophin
provides structural support for the plasma membrane as the
muscle fiber repeatedly contracts and relaxes.
抗肌萎缩蛋白的C端连接着一系列与抗肌萎缩
蛋白相关的糖蛋白 (DAPs) ，进而与收缩细胞的
细胞外基质成分连接.内部端（氨基酸端）连接
肌动蛋白（肌动蛋白是肌细胞的骨架），所以说
抗肌萎缩蛋白是连接肌细胞内部骨架和细胞膜外
的重要桥梁，当肌肉收缩时，它起到稳定肌肉细
胞的作用。
How mutations cause Duchenne
and Becker dystrophy?
There are three types of mutations or
damage of the dystrophin gene:
• Deletions：if one or more entire exons of the
gene are missing;
• Duplications： if parts of the gene are
repeated;
• Point mutations：if single base pairs are
exchanged.
DMD ——Many mutations in the gene disrupt
the reading frame—“out of frame”， and thus
cause the premature abortion（流产） of the
synthesis of the dystrophin,
BMD ——Numerous mutations are “in-frame”,
and conserve the reading frame. Despite a large
internal deletion, a truncated（删节的） but
mostly functional dystrophin is produced. In
these BMD patients, the extent and progression
of the muscle weakness is less severe.
in-frame
如果基因的突变没有完全打乱
“三子一窝”的基因阅读框，
也就说基因字母（核酣酸）缺
失或增加的数量能被3整除，
没有余数。这种情况下抗肌萎
缩蛋白被缩短或者拉长，同时
基因的改变发生在非关键区
域，例如抗肌萎缩蛋白的中
段，使得抗肌萎缩蛋白仍然能
发挥部分的功能，这就形成了
良性的假肥大型进行性肌营养
不良。
BMD
out of frame
假如抗肌萎缩蛋白的基因突变
完全打乱了基因阅读框，也就
是缺失或增加的核酣酸数量不
能被3整除，那么从基因突变的
位点直到抗肌萎缩蛋白的终
点，所有合成的氨基酸都是错
误的，那么不完全的抗肌萎缩
蛋白无法发挥它的正常功能，
这样就形成了杜氏进行性肌营
养不良。
DMD
The comparison between
Becker and Duchenne
Duchenne Muscular Dystrophy:
Dystrophin staining（染色）
Normal dystrophin
Staining around the
rim of muscle fibers
Absent dystrophin
No staining around
the rim of any
muscle fibers
Western blot of dystrophin
BMD
Normal
DMD
Lane 1: Becker dystrophy;
Dystrophin has reduced
abundance but normal size.
Lane 2: Becker dystrophy;
Dystrophin has reduced size
and abundance.
Lane 3: Normal;
Dystrophin has normal size and
amount.
Lane 4: Duchenne dystrophy;
Almost no protein is present.
Lane 5: Duchenne dystrophy;
Dystrophin has severely
reduced abundance.
DMD & BMD
• BMD is a less severe form ,in which
the same protein dystrophin is present
but is abnormal or greatly reduced in
amount .
• An arbitary means of distinguishing the
two disorders depends on whether the
affected person can still walk at age
16 years.
Symptoms症状
Duchenne muscular dystrophy is
the most common form of MD and
primarily affects boys. Onset is
between 3 and 5 years and the
disorder progresses rapidly. Most
boys are unable to walk by age 12.
DMD occurs in about 1 in 3,500
male births, and affects
approximately 8,000 boys and young
men in the United States.
WHAT HAPPENS TO THE VOLUNTARY
MUSCLES OF SOMEONE WITH DMD ?
Difficulty walking, such as being late in learning how to walk
(more than 18 months old), having a waddling gait or
walking on toes or balls of the feet.
• Difficulty running or jumping caused by weakness in leg
muscles.
• Frequent falls, stumbling and difficulty climbing stairs.
• Difficulty standing from a lying or sitting position.
• Reduced endurance.
• Enlarged calf muscles.
• Mild mental retardation, in some cases.
Because of weakened leg muscles, boys with DMD have a
distinctive way of rising from the floor, called the Gowers'
maneuver. They first get on hands and knees, then elevate
the posterior, then "walk" their hands up the legs to raise
their upper body.
The Gower's Maneuver
Other symptoms
• Respiratory Function After a boy with DMD is
about 10 years old, the diaphragm and other muscles that operate the
lungs may weaken, making them less effective in moving air in and out.
• Heart diseasesThe muscle layer (myocardium) of the
heart deteriorates, just as the skeletal muscles do, putting the person
at risk of fatal heart failure.
• Learning disability dystrophin abnormalities in the
brain may cause subtle cognitive and behavioral deficits.
Patients with DMD showdramatic
abnormalities in both cardiac and
skeletal muscle tissue . At the light
microscopic level, some of the
muscle fibers are seen to be
degenerating Necrotic（and often
infiltrated by macrophages of the
immune system.
患DMD的病人在心肌和骨骼肌系统
中表现得相当反常。在显微水平，我
们看到一些肌纤维会逐渐坏死，并且
被免疫系统的巨噬细胞所浸润。
在萎缩的肌纤维间有脂肪浸
润和纤维组织形成。
横切面上见核从周边移入纤
维中央，一些肌纤维萎缩。
在电子显微水平,可以看到肌肉收缩时所产生
的机械压力造成质膜的破裂,质膜片断从细胞表
面流失， 导致细胞内部结构的显著变化，包括：
原生质网状结构的扩张，线粒体的膨胀，肌酶从
胞浆中大量“漏出”并使血清中有关酶相应增加；
肌酶的外溢导致核糖体代偿性合成更多的肌酶，
由于这种代偿作用相当有限，一定时间后肌细胞
即遭受破坏，为增生的结缔组织取代，出现肥大
症状。
Symptoms 症状
Becker muscular dystrophy is basically a milder
form of Duchenne. Boys with Becker MD (very
similar to but less severe than Duchenne MD)
have faulty or not enough dystrophin. The
illness is about 10 times rarer than Duchenne.
BMD affects older boys and young men,
following a milder course than DMD. BMD
occurs in about 1 in 30,000 male births. As with
Duchenne, the pattern of muscle loss in BMD
usually begins with the hips and pelvic area, the
thighs and the shoulders. But in BMD, the rate
of muscle degeneration varies a great deal from
one person to another.
Symptoms症状
The disease progresses with increasing
muscular weakness and debilitation(衰
弱) , finally taking the patient’s life as the
result of respiratory (呼吸)or cardiac
failure（心脏衰竭）
What types of muscular dystrophy
are there?
•
•
•
•
•
•
•
DMD;BMD
Facioscapulohumeral muscular dystrophy (FSH)
Emery-Dreifuss muscular dystrophy (EDMD)
Limb-girdle muscular dystrophy (LGMD)
Oculopharyngeal muscular dystrophy (OPMD)
Distal muscular dystrophy (DD)
Congenital muscular dystrophy (CMD)
Other Types Of muscular dystrophy
Congenital muscular dystrophy
(CMD)——先天肌肉萎缩症
is a rare form of the disease that develops in early
infancy（婴儿时期），and strikes boys and girls
with equal frequency . The disease has been traced to
a deficiency in one of the subunits of the laminin
molecule that forms a key component of the muscle
cell basement membrane。
Congenital muscular
dystrophy
(CMD)
——先天肌肉萎缩症
由层粘连蛋白
（ laminin）缺陷
引起
Other Types Of muscular dystrophy
SCARMD--severe
childhood autosomal
recessive
儿童常染色体隐性肌肉萎缩
症
。A deficiency
of a dystrophinassociated protein could be the
cause of severe childhood
autosomal recessive mus-cular
dystrophy (SCARMD) 由DAG上的
一个单位缺陷引起的
SCARMD的分子病理学
•
Dystrophin是DMD基因的蛋白质产物，近年来人们发现事
实上Dystrophin只是连接肌细胞骨架与细胞外基质的蛋白复合
体的一部分，即Dystrophin要与糖蛋白，如adhalin，β-，γ-，
δ-sarcoglycan等结合形成Dystrophin-糖蛋白复合物
［Dystrophin－associated-glycoprotein(DAG)complex］才能
维持肌肉收缩时的稳定性，Dystrophin缺乏则不能形成此复合
物，使细胞膜不稳定，最终造成肌细胞的坏死，导致DMD的
发生。同理，构成DAG复合物的其它糖蛋白的异常或缺失，
也可影响DAG复合物的形成，这可能是SCARMD的分子基础。
已有很多研究发现了adhalin和γ-sarcoglycan在SCARMD患者
骨骼肌中特异性缺失.
综上，DMD, BMD，CMD,和SCARMD都表
现出该病的严格症状，这表明分子链上的所有
三种组分dystrophin，DAG和Laminin 都是肌
肉功能所必需的。
WHAT TESTS ARE USED TO
DIAGNOSE ?
1/Taking a patient and family history
2/performing a physical examination
3/Have genetic testing
4/Have a muscle biopsy