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| DiseaseID |
HGD41 |
| Genetic
Disorder |
SPINAL MUSCULAR ATROPHY
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| Gene
Name |
SMN1 ,SMN2and VAPB genes |
| Description |
Spinal muscular atrophy (SMA) is a genetic disease that attacks nerve cells, called motor neurons, in your spinal cord. These neurons communicate with your voluntary muscles - the ones you can control, like in your arms and legs. As you lose the neurons, your muscles weaken. This can affect walking, crawling, breathing, swallowing and head and neck control.
SMA runs in families. Parents usually have no symptoms, but still carry the gene. Genetic counseling is important if the disease runs in your family.
There are many types of SMA, and some of them are fatal. Life expectancy depends on the type you have and how it affects your breathing. There is no cure. Medicines and physical therapy help treat symptoms.
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| Symptoms |
In an infant:
Floppy infant
Very weak infant
Little spontaneous movement
Lack of head control
Feeding difficulty
Breathing difficulty
Progressive weakness (older infant to toddler)
In a child:
Nasal speech
Worsening posture
Frequent, increasingly severe respiratory infections
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| Causes |
Spinal muscular atrophy (SMA) is the second leading cause of neuromuscular disease. It is inherited as an autosomal recessive trait (a person must get the defective gene from both parents to be affected) and has an incidence of approximately 4 per 100,000 people.
In its most severe form (SMA type I, also called Werdnig-Hoffman disease), infants are born floppy with weak, thin muscles and feeding and breathing problems. Their lifespan seldom exceeds 2 to 3 years. Infants with SMA type II have less severe symptoms during early infancy, but they become progressively weaker with time. Survival time with type II is longer, but the disease kills most of those affected while they are still children.
SMA type III is the least severe form of the disease, and symptoms may not appear until the second year of life. Often, weakness is first noted in the shoulder muscles and proximal leg muscles. Weakness is progressive and will eventually become profound, but children with type III disease may survive into early adulthood.
Rarely, SMA may begin in adulthood. This is usually a milder form of the disease. This form may be inherited in an autosomal dominant (only one copy of the gene is needed for the disease to occur) or autosomal recessive manner.
Family history of spinal muscular atrophy is a risk factor for all types of the disorder. |
| Diagnosis |
Diagnosis can be done on the following examinations and tests:
• A family history of neuromuscular disease
• Absent deep tendon reflexes
• Flaccid muscles
• Muscle fasciculation
• Fasciculation of tongue muscle
• Elevated CPK levels
Tests:
• Muscle biopsy
• Electromyography
• MRI of the spine
• DNA testing to confirm diagnosis
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| Treatment |
There is no treatment for the progressive weakness caused by the disease. Supportive care is important. Attention must be paid to the respiratory system, because affected people have difficulty clearing secretions. Respiratory complications are common.
Physiotherapy is important to prevent contractures and scoliosis. Bracing may be necessary. |
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