Muscular Dystrophy Flashcards
The muscular dystrophies are a class of inherited disorders of metabolism characterized by muscle ____ and ____
degeneration; weakness
True or false? in muscular dystrophies, symptoms are only expressed in muscle
false; in tissue too
_____ is a characteristic of all of the muscular dystrophies. Serum creatine kinase activity is elevated in many of the muscular dystrophies
Creatinuria
Defects in the structure and function of ____ _____ appear to be associated with all of the muscular dystrophies
cellular membranes
These two muscular dystrophies are X-linked
duchenne muscular dystrophy and becker muscular dystrophy
X-linked muscular dystrophies primarily affect males or females?
males; female carriers are occasionally mildly affected
What is the incidence of Duchenne and Becker muscular dystrophies?
1 in 5200 live male births
What is the primary defect in Duchenne and Becker muscular dystrophies?
dystrophin; gene is deleted from the short arm of the X chromosome
The Dystrophin gene is one of the largest recognized to date: ____kb, ____ exons
2300; 79
Dystrophin is associated with the ____ of normal muscle
sarcolemma
In Duchenne patients, dystrophin is ____; in Becker patients, dystrophin is ____ _____
absent; significantly reduced
Dystrophin interacts with what?
actin, syntrophin, B-dystroglycan, and others
Deficiency in Dystrophin may affect the integrity of the plasma membrane resulting in what?
increased osmotic fragility or permitting excessive Ca2+ influx
A clinical sign of MD is a delay in what type of development?
gross motor development
note: delays appear by second year of life
When do difficulty walking, running, climbing stairs, and riding a tricycle appear in MD patients?
ages 3-5
Progressive weakness with waddling gait, lordosis, difficulty rising from a sitting supine position (Gower’s sign) are all signs of MD. True or false?
true
Calf muscle hypertrophy occurs in MD patients when ____ and ____ ____ completely replace muscle
fat; connective tissue
Scoliosis; contractors of ____ bands, ___ joints and ___ cords, and joint deformities are seen in MD patients
iliotibial; hip; heal
Inability to ambulate by about age ____ mild mental retardation is seen in MD patients
12
Respiratory and accessory muscles involved in end stage with cardiomegaly usually occurs at age ___-___ in MD patients
20-30
In regards to organ systems in MD patients, what abnormalities are seen in the cardiac system?
ECG abnormalities and left ventricle myocardial fibrosis
In regards to organ systems in MD patients, what abnormalities are seen in the GI system?
pathologic involvement of smooth muscle leading to acute gastric dilation: vomiting, pain, and dissension which may lead to death
In MD patients, what abnormalities are seen in the CNS?
IQ generally 1 standard deviation below average
In MD patients Creatine Kinase has marked elevation in first years of life, before obvious clinical manifestations. True or false?
true
CK levels of ___-____ X normal are expected by 3 years of age
50-100
CK levels drop about ____% after age 3 due to decreasing healthy muscle tissue
20
CK less than 10 X normal at any age is strong evidence for a diagnosis of MD
false; strong evidence against a diagnosis
Electromyography of MD patients typically indicates a myopathy characterized by what?
early recruited, short-duration, low amplitude, polyphasic motor unit potentials
Muscle biopsy of a MD patient shows what?
variability in muscle fiber size including both small and hypertrophied fibers
Muscle biopsy in MD patients shows small groups of ____ and ____ fibers and large, opaque, darkly stained fibers are frequent as a result of _____ _____
regenerating; necrotic; segmental hypercontraction
___ gradually replaces lost muscle fibers in MD patients
Fat
_____ analysis is the definitive diagnosis
Dystrophin
Absence of dystrophin can be demonstrated by ____ ____ analysis
western blot
note: prenatal testing of amniotic fluid or chorionic villus sampling using cDNA probes is also available
By age ___, most boys require leg braces and surgery may be required to reduce _____
9; scoliosis
Prednisone improves what?
muscle mass and muscle function
What is the mechanism by which prednisone works?
may act through suppression of cytotoxic T-lymphocytes thus reducing invasion of muscle tissue by lymphocytes
In regards to a myoblast tranfer study in 1995, ___% of the subjects showed no improvement in muscle strength
92
