Muscular dystrophy

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Muscular dystrophy
Classifications and external resources
ICD-10 G71.0
ICD-9 359.0-359.1
MedlinePlus 001190
eMedicine orthoped/418 

Muscular Dystrophy is a broad term that describes a genetic group of more than 30 genetic and hereditary muscle diseases; It is characterized by progressive skeletal muscle weakness, defects in muscle proteins, and the death of muscle cells and tissue. In some forms of Muscular Dystrophy, cardiac and smooth muscles are affected. Muscular Dystrophy is the most well known of hereditary diseases.

Contents

[edit] Genetic cause

This condition is inherited in an X-linked recessive pattern and is considered X-linked if the mutated gene that causes the disorder is located on the X chromosome, one of the two sex chromosomes and is considered sex-linked. In males (who have only one X chromosome) one altered copy of the gene in each cell is sufficient to cause the condition. In females (who have two X chromosomes) a mutation must be present in both copies of the gene to cause the disorder. Males are affected by X-linked recessive disorders much more than females. A characteristic of X-linked inheritance is that fathers cannot pass X-linked traits to their sons.

In about two thirds of cases, an affected male inherits the mutation from a mother who carries one altered copy of the DMD gene. The other one third of cases probably result from new mutations in the gene. Females who carry one copy of a DMD mutation may have some signs and symptoms related to the condition (such as muscle weakness and cramping), but these are typically milder than the signs and symptoms seen in affected males.

The most common forms are Duchenne muscular dystrophy and Becker's muscular dystrophy This form is caused by mutations of the gene for the dystrophin protein and leads to an overabundance of the enzyme creatine kinase. The dystrophin gene is the second largest gene in mammals.

[edit] Symptoms

Principal symptoms include but are not limited to:

  • Progressive Muscle Wasting
  • Weakness
  • Loss of Function in Muscle Skills
  • Poor Balance
  • Frequent Falls
  • Walking Difficulty
  • Waddling Gait
  • Calf Pain
  • Limited Range of Movement
  • Joint Contractures
  • Cataracts
  • Frontal Baldness
  • Drooping Eyelids (ptosis)
  • Drooling
  • Gonadal Atrophy
  • Mental Impairment (with myotonic dystrophy)
  • Scoliosis (curved spine)


Some types of Muscular Dystrophy can involve the heart muscle, causing cardiomyopathy or arrhythmias.

[edit] Diagnosis

The diagnosis of Muscular Dystrophy is based the results of muscle biopsy. In some cases, a DNA blood test may be all that is needed.

A physical examination and your medical history will help the doctor determine the type of muscular dystrophy. Specific muscle groups are affected by different types of muscular dystrophy.

Often, there is a loss of muscle mass (wasting), which may be hard to see because some types of muscular dystrophy cause a build up of fat and connective tissue that makes the muscle appear larger. This is called pseudohypertrophy.

[edit] Prognosis

The prognosis for people with Muscular Dystrophy varies according to the type and progression of the disorder. Some cases may be mild and progress very slowly over a normal lifespan, while others produce severe muscle weakness, functional disability, and loss of the ability to walk. Some children with Muscular Dystrophy die in infancy while others live into adulthood with only moderate disability. The muscles affected vary, but can be around the pelvis, shoulder, face or elsewhere. Muscular dystrophy can affect adults, but the more severe forms tend to occur in early childhood.

[edit] Treatment

There is no known cure for muscular dystrophy. Inactivity (such as bed-rest and even sitting for long periods) can worsen the disease. Physical therapy and orthopedic instruments (e.g., wheelchairs, standing frames) may be helpful.

There is no specific treatment for any of the forms of muscular dystrophy. Physical therapy to prevent contractures (a condition in which shortened muscles around joints cause abnormal and sometimes painful positioning of the joints), orthoses (orthopedic appliances used for support) and corrective orthopedic surgery may be needed to improve the quality of life in some cases. The cardiac problems that occur with Emery-Dreifuss muscular dystrophy and myotonic muscular dystrophy may require a pacemaker. The myotonia (delayed relaxation of a muscle after a strong contraction) occurring in myotonic muscular dystrophy may be treated with medications such as quinine, phenytoin, or mexiletine.

[edit] Types of Muscular Dystrophy

  • Becker's muscular dystrophy- age at onset: two to 16 years; symptoms are almost identical to Duchenne but less severe; progresses more slowly than Duchenne; survival into middle age.
  • Congenital muscular dystrophy - age at onset: birth; symptoms include general muscle weakness and possible joint deformities; disease progresses slowly; shortened life span.
  • Duchenne muscular dystrophy - age at onset: two to six years; symptoms include general muscle weakness and wasting; affects pelvis, upper arms, and upper legs; eventually involves all voluntary muscles; survival beyond 20s is rare. However recent advances in medical care has caused the survival age to increase significantly.
  • Distal muscular dystrophy - age at onset: 40 to 60 years; symptoms include weakness and wasting of muscles of the hands, forearms, and lower legs; progress is slow; rarely leads to total incapacity.
  • Emery-Dreifuss muscular dystrophy - age at onset: childhood to early teens; symptoms include weakness and wasting of shoulder, upper arm, and shin muscles; joint deformities are common; progress is slow; sudden death may occur from cardiac problems
  • Facioscapulohumeral muscular dystrophy - age at onset: teens to early adults; symptoms include facial muscle weakness and weakness with some wasting of shoulders and upper arms; progress is slow, with periods of rapid deterioration; life span may be many decades after onset.
  • Limb-girdle muscular dystrophy - age at onset: late childhood to middle age; symptoms include weakness and wasting, affecting shoulder girdle and pelvic girdle first; progress is slow; death is usually due to cardiopulmonary complications.
  • Myotonic muscular dystrophy - age at onset: 20 to 40 years; symptoms include weakness of all muscle groups accompanied by delayed relaxation of muscles after contraction; affects face, feet, hands, and neck first; progress is slow, sometimes spanning 50 to 60 years.
  • Oculopharyngeal muscular dystrophy - age at onset: 40 to 70 years; symptoms affect muscles of eyelids and throat causing weakening of throat muscles, which in time causes inability to swallow and emaciation from lack of food; progress is slow.

[edit] Neuromuscular diseases

Classified as Muscular Dystrophy

Spinal Muscular Atrophies:

  • Amyotrophic Lateral Sclerosis, ALS, or Lou Gehrig's Disease
  • Infantile Progressive Spinal Muscular Atrophy, SMA Type 1
  • Intermediate Spinal Muscular Atrophy, SMA Type 2
  • Juvenile Spinal Muscular Atrophy, SMA Type 3
  • Adult Spinal Muscular Atrophy, SMA Type 4

Inflammatory Myopathies:

Diseases of Peripheral Nerve:

  • Charcot-Marie Tooth Disease
  • DeJerine-Sottas Disease
  • Friedreich's Ataxis

Diseases of the Neuromuscular Junction:

Metabolic Diseases of the Muscle:

  • Acid Maltase Deficiency
  • Carnitine Deficiency
  • Carnitine Palmityl Transferase Deficiency
  • Debrancher Enzyme Deficiency
  • Lactate Dehydrogenase Deficiency
  • Mitochondrial Myopathy
  • Myoadenylate Deaminase Deficiency
  • Phosphorylase Deficiency
  • Phosphofructokinase Deficiency
  • Phosphoglycerate Kinase Deficiency

Less Common Myopathies:

[edit] 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. Six years later, another scientist reported on two brothers who developed generalized weakness, muscle damage, and replacement of damaged muscle tissue with fat and connective tissue. At that time the symptoms were thought to be signs of tuberculosis.

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.

[edit] References

[edit] External links

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