Duchenne muscular dystrophy (DMD) is inherited muscle disorder mainly affecting males. It is the most common of all nine muscular dystrophies. The disease is characterized by progressive degeneration and death of muscle fibers. Duchenne muscular dystrophy occurs due to mutation (defect) in the gene that produces protein called dystrophin. The function of dystrophin is to help the muscle work properly and to maintain its shape.
Lack of dystrophin due to gene mutation causes gradual death of muscle cell. This leads to various signs and symptoms such as difficulty in walking, frequent falls, enlargement of calf muscles, weakness of muscles of hip, leg, and arm muscles etc.The affected male child usually has to use wheelchair by the age of 12.
There is no cure for duchenne muscular dystrophy. Treatment is aimed to reduce severity of symptoms and extend life. Patients die early in the third decade of their life due to respiratory or cardiac failure.
What Is The Cause Of Duchenne Muscular Dystrophy?
Duchenne muscular dystrophy is a genetically inherited disease. It is an X-linked gene mutation disorder mainly affecting male child. The abnormal gene is present on X-chromosome which is passed on to the child from mother. Normally the gene (MIM 300377) is involved in making a protein called dystrophin which gives structural support to muscle fibers so that they remain intact and function well.However, absence of this protein in duchenne muscular dystrophy causes progressive degradation and death of muscle as the child grows older.
Boys are mainly affected because boys have one X and one Y sex chromosome. X is inherited from mother and Y is inherited from father in boys. Hence if the boy inherits a defective gene for DMD from his mother he will develop duchenne muscular dystrophy. Since girls have two XX chromosomes, even if one X is having defective gene from the mother the other normal copy of gene from other X chromosome is enough to make dystrophin protein and prevent the condition. Girls are not affected and remain asymptomatic but they become carrier if they inherit the defective gene from their mother.
Signs And Symptoms Of Duchenne Muscular Dystrophy
The clinical symptoms of muscle weakness in duchenne muscular dystrophy develop during early childhood, usually before the age of 4 years. Onset of symptoms is progressive. First the muscles of hip, pelvis, thigh and shoulder become weak. Later on weakness spreads to muscles of arm, leg and trunk.
- Walking is often delayed and the gait is clumsy with frequent falls. The child may have trouble while climbing stairs or getting up from sitting position.
- Most children have waddling gait because of early weakness in hip and thigh muscles. To keep the balance the child sticks out his belly and pulls his shoulder backwards. This position is called lumbar lordosis.
- Enlarged calf muscles in toddlers.
- The muscles around joint become stiff. This causes limitation in movement of the child. These children often walk on their toes or on ball of their feet.
- Some children may have learning difficulty but it does not worsen and it is not severe.
- By the age of 12 or 13, the child losses his ability to walk. He is confined to wheelchair. Patient after a period of time will develop scoliosis a fixed deformity of spine.
- Weakness in lung muscles will cause difficulty in breathing. It increases risk of frequent infection in respiratory tract.
- Absence of dystrophin weakens heart muscles leading to cardiomyopathy.
Diagnosis And Treatment Of Duchenne Muscular Dystrophy
Diagnosis of duchenne muscular dystrophy is reached by taking family history, clinical examination of the child, and reviewing results of several tests. Certain blood tests and biopsy of muscles will help in confirming the diagnosis.
Blood test called CPK (creatine phosphokinase) is used to determine DMD. CPK is enzyme that increases in blood when muscles are damaged or become weak. High level of CPK is a pointer of some muscular pathology. Blood is also checked for abnormal gene.
Further muscle biopsy will accurately help in determining the type of muscular dystrophy.
Duchenne muscular dystrophy is not a curable disorder. The goal of treatment is to control the symptoms and keep the muscle active so that the patient can live best possible quality of life till he lives.
Following treatment modes may be useful for patient with DMD:
- Physiotherapy is beneficial to prevent contractures and maintain movement as long as possible. Parents are taught to stretch the child’s heel cords and hip flexor muscles on daily basis. Joint stretching passively can help to prevent worsening of contractures.
- Splints and braces are used to keep the leg fully extended. Appropriate use of braces delays the child losing movement and use of wheelchair by few years.
- Use of special boot will help the child to maintain good stability.
- As the child attains 12 -13 years he may need wheelchair.
- Steroids medication is used to slow down the progression of duchenne muscular dystrophy. Steroids are started on first clinical suspicion of the disorder. Steroids help the muscles to remain strong and function well in these patients.
- Patient may require reconstructive surgery if the tendons and joints become tight and deformed.
- Patient may need medicines to reduce high blood pressure and heart related problems.
During the later stage of disease when the lung function becomes weak, patient may require ventilator to prolong life.
Prognosis: Duchenne muscular dystrophy is a fatal condition. There is no therapy that can stop progression of the disease. Most patients die in their 20’s. With proper and diligent care some patients may survive in their 30’s. During the later phase of disease, patient may be completely bed ridden and he may need full time care.