DUCHENNE MUSCULAR DYSTROPHY

Duchenne muscular dystrophy (DMD) is a rapidly progressive form of muscular dystrophy that occurs primarily in boys.

  • It is caused by an alteration (mutation) in a gene, called the DMD gene that can be    
           inherited in families in an X-linked recessive fashion, but it often occurs in people from 
           families without a known family history of the condition

  • Individuals who have DMD have progressive loss of muscle function and weakness, which 

            begins in the lower limbs. The DMD gene is the second largest gene to date, which encodes    
            the muscle protein, dystrophin.

Frequency:  1/3500 Male births

Phenotype/ Characteristics:

Duchenne muscular dystrophy is inherited in an X-linked recessive pattern. Males have only one copy of the X chromosome from their mother and one copy of the Y chromosome from their father. If their X chromosome has a DMD gene mutation, they will have Duchenne muscular dystrophy. Females, on the other hand, have two copies of the X chromosomes. Since females have two copies of this gene, if one copy does not work, they have a second back up copy to produce the dystrophin protein.

Understanding the inheritance of DMD!

Each son of a female carrier has a 50% chance of inheriting DMD through his mother’s faulty X chromosome and each daughter has a 50% chance of being a carrier of the disorder in the same way. Soon after the diagnosis of DMD it is essential that genetic counselling is arranged, together with appropriate tests for those members of the family who are at risk of being carriers. Genetic counselling provides information on the inheritance pattern, risks to other family members, and the ‘prognosis’ (likely outcome of the disorder). This service also provides information about diagnostic testing, including prenatal testing, as well as carrier testing.

What are the symptoms of Duchenne muscular dystrophy?

>  First noticeable symptom is delay of motor milestones, including sitting and standing 

    independently.

> The mean age for walking in boys with Duchenne muscular dystrophy is 18 months.

> There is progressive muscle weakness of the legs and pelvic muscles, which is associated 
    with a loss of muscle mass (wasting).
>  Calf muscles initially enlarge and the enlarged muscle tissue is eventually replaced with fat  
     and connective tissue (pseudohypertrophy).
>  Symptoms usually appear in boys aged 1 to 6. There is a steady decline in muscle strength 
     between the ages of 6 and 11 years. By age 10, braces may be required for walking, and by
     age 12, most boys are confined to a wheelchair. Bones develop abnormally, causing 
     skeletal deformities of the spine and other areas.
>   Muscular weakness and skeletal deformities frequently contribute to breathing disorders
> Cardiomyopathy (enlarged heart) occurs in almost all cases, beginning in the early teens in  
     some, and in all after the age of 18 years.
> Intellectual impairment may occur, but it is not inevitable and does not worsen as the disorder 
    progresses.
> Few individuals with DMD live beyond their 30s. Breathing complications and     

    cardiomyopathy are common causes of death

Diagnosis:

Ø  A clinical diagnosis may be made when a boy has progressive symmetrical muscle weakness.

Ø  The symptoms present before age 5 years, and they often have extremely elevated creatine kinase blood levels (which are described below) .

Ø   If untreated, the affected boys become wheelchair dependent before age 13 years.

Ø  A muscle biopsy (taking a sample of muscle) for dystrophin studies can be done to look for abnormal levels of dystrophin in the muscle.

Ø  Genetic testing (looking at the body's genetic instructions) on a blood sample for changes in the DMD gene can help establish the diagnosis of Duchenne muscular dystrophy without performing a muscle biopsy.

Ø  For the remaining individuals, a combination of clinical findings, family history, blood creatine kinase concentration and muscle biopsy with dystrophin studies confirms the diagnosis.

Treatment:

Ø  Treatment for Duchenne muscular dystrophy is aimed at the symptoms.

Ø  Aggressive management of dilated cardiomyopathy with anti-congestive medications is used, including cardiac transplantation in severe cases.

Ø  Assistive devices for respiratory complications may be needed, especially at night.

Ø  The medication prednisone — a steroid — is given to improve the strength and function of individuals with DMD. Prednisone has been shown to prolong the ability to walk by 2 to 5 years. However, the possible side effects of prednisone include weight gain, high blood pressure, behavior changes, and delayed growth.

Ø   A synthetic form of prednisilone, called Deflazacort, is used in Europe and believed to have fewer side effects than prednisone.

Ø   A medication called cyclosporine has been used and has improved clinical function in children, but its use is controversial due to cyclosporine-induced myopathy.

Ø  Oxandrolone, a medication used in a research study, has similar effects to prednisone with fewer side effects. 

Recommendations/advices:

--> Communication is a key word in the coping process. If parents can speak openly and honestly with each other, sharing concerns and discussing ways to meet challenges, the whole family will benefit. 

-->  Be open and approachable. Encourage him to discuss his needs, to learn to ask others for assistance when he needs it and to politely refuse when he can manage independently.

-->  A healthy diet, with restriction on foods containing high levels of fat and sugar, and including plenty of fluids, fruit and vegetables can be encouraged.

--> Encourage special interests, physical exercise such as swimming, according to his mobility, and relationships with peers.

-->  Always remember that he needs support, love, a warm and caring family environment and not least, the encouragement to live life as fully as possible with his friends and family.

--> Rather than leaving the majority of the additional responsibilities to one family member, it is advisable to involve all family members as much as possible.

 --> Creating new friendships with other DMD families (or families living with other disabilities) can be rewarding for all concerned

References:

Learning About Duchenne Muscular Dystrophy (2010). Retrieved on March 12, 2013 from http://www.genome.gov/19518854

Duchenne Muscular Dystrophy (2011). Retrieved on March 12, 2013 from http://www.umm.edu/ency/article/000705.htm

Photos from:
http://www.loyarburok.com/wp-content/uploads/2011/05/Duchenne.jpg
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