MUSCULAR DYSTROPHY: A REVIEW

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About Authors:
Naga Manjusha. Somavarapu*, Ramya krishna. Barma
Department Of Pharmacology, Shri Vishnu College Of Pharmacy,
Bhimavaram, W. G. Dist., A. P.
snmanjusha8@gmail.com

Abstract:
Muscular dystrophy is one of the rare diseases that cause progressive weakness and degeneration of skeletal muscles used during voluntary movement. There are many different types of muscular dystrophy based on the age of onset, severity and pattern of inheritance, of which duchenne and becker muscular dystrophies being more prevalent. The absence or abnormality of dystrophin, a protein which forms a complex with extracellular matrix to provide mechanical reinforcement to the structure of the sarcolemma and thereby protecting the membrane from the stress or tearing during contraction is the main cause of muscular dystrophy. Muscular dystrophy can be diagnosed by blood & urine tests, muscle biopsies, DNA (genetic) testing, and diagnostic imaging and neurophysiology studies. Treatment includes various therapies such as respiratory therapy, physical therapy, speech therapy, occupational therapy, corrective surgery, drug therapy, and gene therapy.

REFERENCE ID: PHARMATUTOR-ART-2161

PharmaTutor (ISSN: 2347 - 7881)

Volume 2, Issue 5

Received On: 15/03/2014; Accepted On: 23/03/2014; Published On: 01/05/2014

How to cite this article: NM Somavarapu, RK Barma; Muscular Dystrophy: A Review; PharmaTutor; 2014; 2(5); 19-30

Introduction:
Muscular dystrophy (MD) refers to a group of more than 30 genetic diseases that cause progressive weakness and degeneration of skeletal muscles used during voluntary movement. The word dystrophy is derived from the Greek dys, which means "difficult" or "faulty," and troph, or "nourish." These disorders vary in age of onset, severity, and pattern of affected muscles. All forms of MD grow worse as muscles progressively degenerate and weaken. Many individuals eventually lose the ability to walk.3

People who have muscular dystrophy may have trouble breathing or swallowing. Their limbs may also draw inward and become fixed in that position — a problem called contracture. Some varieties of the disease can also affect the heart and other organs.

While there is no cure for muscular dystrophy, medications and therapy can slow the course of the disease.1

History:
The first historical account of muscular dystrophy appeared in 1830, when Sir Charles Bell wrote an essay about an illness that caused progressive weakness in boys.

In the 1850s, descriptions of boys who grew progressively weaker, lost the ability to walk, and died at an early age became more prominent in medical journals. In the following decade, French neurologist Guillaume Duchenne gave a comprehensive account of 13 boys with the most common and severe form of the disease (which now carries his name—Duchenne muscular dystrophy). It soon became evident that the disease had more than one form, and that these diseases affected people of either sex and of all ages.3

In June 1950, Paul Cohen, a prominent New York business leader living with a form of muscular dystrophy, invited a group of individuals to meet in his Rye, N.Y., office. Each had a personal connection to muscular dystrophy, and the gathering focused on the urgent need to raise funds to advance research seeking treatments and cures for muscular dystrophy. The group so vested in the fight against neuromuscular diseases & formed the organization that became the Muscular Dystrophy Association (MDA).

Prevalence:
MD occurs worldwide, affecting all races. Its incidence varies, as some forms are more common than others. It is most common form in children, Duchenne muscular dystrophy, affects approximately 1 in every 3,500 to 6,000 male births each year in the United States. Many muscular dystrophies are familial, meaning there is some family history of the disease.3

Becker muscular dystrophy (BMD) is a milder form of muscular dystrophy. BMD affects about 1 in 18,500 male births.2

Pathophysiology:
Muscles are composed mostly of protein in a highly organized system from large groups to small fibers. Muscle units are separated from other muscle groups by plasma membranes called the sarcolemma and the cytoplasm within is called the sarcoplasm. Within the sarcoplasm are multiple long protein bundles called myofibrils, composed of parallel myofilaments which is where most of the action takes place.


In the myofilaments are contractile proteins called myosin (thick filaments), and actin (thin filaments). When signaled, the actin and myosin interlock and slide over each other to stretch or slide into one another to contraction. They are signaled from the nervous system followed by a series of chemical reactions involving ATP, calcium, sodium and potassium ions.

Aside from the contractile proteins, there are regulatory proteins called tropomyosin and troponin which act like a switch to determine when to contract and when to relax. On the muscle fiber the ‘I band’ is the space between the myosin (thick) filaments, where lies only the thin filaments. In the middle of each ‘I band’ is a dark disc called the ‘Z disc’ made of titan, (elastic filament), which is connected to the sarcolemma by the cytoskeleton. The space between each Z disc, where these filaments interact, is called the sarcomere. As the muscle contracts the ‘I band” shrinks and the sarcomere shortens and as the Z disc’s come closer together pulling on the sarcolemma shortening the cell. This is how the muscle contracts. One of the most clinically important accessory proteins here is dystrophin which is located just under the sarcolemma in the cytoplasm in the area of the ‘I band’. It is produced by specific genes and links the actin filaments to the protein extracellular matrix in the membrane known as the dystrophin-associated protein complex.

Elements of the dystrophin gene and the protein structure have been identified, yet the exact functional role is still a bit unclear. However as research continues it is thought that its primary function is to provide mechanical reinforcement to the structure of the sarcolemma and thereby protecting the membrane from the stress or tearing during contraction. If dystrophin is defective or absent, the membrane breaks down which then substances and molecules like proteins and enzymes leak out of the fiber into circulation. These enzymes and chemicals that leak out are responsible for certain chemical reactions and necessary for energy production for muscle contraction. At the same time the extracellular substances leak into the fiber through the broken down membrane damaging the fiber and disrupting the process of muscle contraction and may cause irreparable damage.

The absence or abnormality of dystrophin results in a condition known as Muscular Dystrophy.

Muscular Dystrophy is a crippling disease resulting from mutated genes which slowly wastes away muscle tissue. Without dystrophin to help protect the fiber membrane keeping it intact, and assisting to create energy, the muscles begin to degenerate and atrophy, being replaced by fat and fibrous scar tissue creating fascia adhesions throughout the body.4

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