Duchenne muscular dystrophy – Wikipedia, the free encyclopedia

Duchenne muscular dystrophy Classification and external resources

Histopathology of gastrocnemius muscle from patient who died of pseudohypertrophic muscular dystrophy, Duchenne type. Cross section of muscle shows extensive replacement of muscle fibers by adipose cells.

Duchenne muscular dystrophy (DMD) is a recessive X-linked form of muscular dystrophy, affecting around 1 in 3,600 boys, which results in muscle degeneration and eventual death.[1] The disorder is caused by a mutation in the dystrophin gene, the largest gene located on the human X chromosome, which codes for the protein dystrophin, an important structural component within muscle tissue that provides structural stability to the dystroglycan complex (DGC) of the cell membrane. While both sexes can carry the mutation, females rarely exhibit signs of the disease.

Symptoms usually appear in male children before age 6 and may be visible in early infancy. Even though symptoms do not appear until early infancy, laboratory testing can identify children who carry the active mutation at birth.[2] Progressive proximal muscle weakness of the legs and pelvis associated with a loss of muscle mass is observed first. Eventually this weakness spreads to the arms, neck, and other areas. Early signs may include pseudohypertrophy (enlargement of calf and deltoid muscles), low endurance, and difficulties in standing unaided or inability to ascend staircases. As the condition progresses, muscle tissue experiences wasting and is eventually replaced by fat and fibrotic tissue (fibrosis). By age 10, braces may be required to aid in walking but most patients are wheelchair dependent by age 12. Later symptoms may include abnormal bone development that lead to skeletal deformities, including curvature of the spine. Due to progressive deterioration of muscle, loss of movement occurs, eventually leading to paralysis. Intellectual impairment may or may not be present but if present, does not progressively worsen as the child ages. The average life expectancy for patients afflicted with DMD is around 25.[1]

The disease was first described by the Neapolitan physician Giovanni Semmola in 1834 and Gaetano Conte in 1836.[3][4][5] However, DMD is named after the French neurologist Guillaume Benjamin Amand Duchenne (18061875), who, in the 1861 edition of his book "Paraplegie hypertrophique de l'enfance de cause cerebrale", described and detailed the case of a boy who had this condition. A year later, he presented photos of his patient in his "Album de photographies pathologiques." In 1868 he gave an account of 13 other affected children. Duchenne was the first who did a biopsy to obtain tissue from a living patient for microscopic examination.[6][7]

Duchenne muscular dystrophy (DMD) is caused by a mutation of the dystrophin gene at locus Xp21. Dystrophin is responsible for connecting the cytoskeleton of each muscle fiber to the underlying basal lamina (extracellular matrix) through a protein complex containing many subunits. The absence of dystrophin permits excess calcium to penetrate the sarcolemma (cell membrane).[8] Alterations in these signalling pathways cause water to enter into the mitochondria which then burst. In skeletal muscle dystrophy, mitochondrial dysfunction gives rise to an amplification of stress-induced cytosolic calcium signals and an amplification of stress-induced reactive-oxygen species (ROS) production. In a complex cascading process that involves several pathways and is not clearly understood, increased oxidative stress within the cell damages the sarcolemma and eventually results in the death of the cell. Muscle fibers undergo necrosis and are ultimately replaced with adipose and connective tissue.

DMD is inherited in an X-linked recessive pattern. Females will typically be carriers for the disease while males will be affected. Typically, a female carrier will be unaware they carry a mutation until they have an affected son. The son of a carrier mother has a 50% chance of inheriting the defective gene from his mother. The daughter of a carrier mother has a 50% chance of being a carrier or having two normal copies of the gene. In all cases, the father will either pass a normal Y to his son or a normal X to his daughter. Female carriers of an X-linked recessive condition, such as DMD, can show symptoms depending on their pattern of X-inactivation.

Duchenne muscular dystrophy is caused by mutations in DMD gene which codes for protein dystrophin. DMD gene is located on the short arm of the X chromosome (Xp21.2-p21.1).[9] Duchenne muscular dystrophy has an incidence of 1 in 3,600 male infants.[9] Mutations within the dystrophin gene can either be inherited or occur spontaneously during germline transmission.

The main symptom of Duchenne muscular dystrophy, a progressive neuromuscular disorder, is muscle weakness associated with muscle wasting with the voluntary muscles[citation needed] being first affected, especially affecting the muscles of the hips, pelvic area, thighs, shoulders, and calf muscles. Muscle weakness also occurs in the arms, neck, and other areas, but not as early as in the lower half of the body. Calves are often enlarged. Symptoms usually appear before age 6 and may appear as early as infancy. The other physical symptoms are:

According to Lewis P. Rowland, in the anthology Gene Expression In Muscle, if a boy is affected with Duchenne muscular dystrophy (DMD), the condition can be observed clinically from the moment he takes his first steps. It becomes harder and harder for the boy to walk; his ability to walk usually completely disintegrates between the time the boy is 9 to 12 years of age. Most men affected with DMD become essentially paralyzed from the neck down by the age of 21.[10] Muscle wasting begins in the legs and pelvis, then progresses to the muscles of the shoulders and neck, followed by loss of arm muscles and respiratory muscles. Calf muscle enlargement (pseudohypertrophy) is quite obvious. Cardiomyopathy (DCM) is common, but the development of congestive heart failure or arrhythmias (irregular heartbeats) is only occasional.

See the article here:
Duchenne muscular dystrophy - Wikipedia, the free encyclopedia