Spinal muscular atrophy (SMA) is an autosomal recessive genetic disorder that hampers with a child’s ability to move by affecting motor nerve cells that control voluntary muscle movement. This disease is progressive in nature and is caused by the loss of specialized motor neurons in the spinal cord and the brainstem. This affects a child’s ability to perform motor activities such as sitting up, jumping, walking, crawling, and controlling head movement. SMA mainly causes muscle wasting and weakness. Moreover, some people who suffer from severe cases of SMA face difficulty in breathing and swallowing as the muscles used for these functions are also affected. Below is some information on different types; diagnosis and treatments of SMA that can help families of the affected children understand the disease better.
Types of SMA
SMA can be classified into five different types: 0, I, II, III, and IV. Each type is categorized on the basis of different symptoms, and physicians often determine the type by understanding the symptoms.
- Type 0
Type 0 SMA is one of the most severe types. It is identified on the basis of symptoms such as decreased fetal movements, joint abnormalities, inability to swallow properly, and respiratory failure. This type occurs in a child before birth or within the first few months of birth.
- Type I
Type I SMA is also called the Werdnig-Hoffman disease. It is one of the severe types of SMA that affects a person since their birth or within the first few months after birth. It is quite similar to the type 0 SMA as type I affected infants also face delayed physical developments. Children with this type exhibit symptoms such as breathing and swallowing problems that can cause choking. Other symptoms include diminished limb movements, fasciculation, tremors, hypotonia (severely reduced muscle tone), and lack of tendon reflexes.
- Type II
Type II SMA often occurs when a child’s age is between 6 and 18 months. Although children with type II SMA can manage to sit without needing support, they do require assistance to get to a seated position. Individuals who are affected by type II SMA are unable to stand and walk without aid.
- Type III
Type III SMA is a juvenile type and is also known as the Kugelberg-Welander disease. The effects of a type III SMA are mild. Type II SMA affected individuals can walk or stand without any assistance; however, they struggle while climbing stairs and are often unable to do so. Other symptoms of this type include abnormal gait, tremors in the fingers, and difficulty in rising from a chair. Type II SMA affected individuals can walk or stand without any assistance; however, they struggle while climbing stairs and are often unable to do so. Other symptoms of this type include abnormal gait, tremors in the fingers, and difficulty in rising from a chair.
- Type IV
Type IV SMA often occurs when an individual is over 30 years of age. Symptoms of type IV SMA include mild to moderate muscle weakness, mild breathing problems, twitching, and tremors.
Diagnoses of SMA
A physician first observes the symptoms of SMA in an affected individual before deciding the diagnosis method. This process takes place by conducting a thorough physical exam that also includes the analysis of the patient’s and their family’s medical history. For an accurate diagnosis, the physician conducts certain tests, such as the ones mentioned below.
- Genetic testing
In genetic testing, the physician checks for any defects or mutations in two genes for diagnosing SMA. These genes are the SMN1 gene, which is responsible for the production of the survival motor neuron protein, and neuronal apoptosis inhibitory protein gene (NAIP).
- Electrodiagnostic tests
Electrodiagnostic tests include electromyography (EMG) and nerve conduction studies. In EMG, electrodes are inserted into the skin for measuring the bioelectrical activity of muscles. This helps in identifying any nerve damage along with the diagnosis. As for nerve conduction studies, electrodes are placed on the skin over a peripheral or sensory-motor nerve. Subsequently, a small electric shock is emitted that causes the electrical impulse to stimulate motor or sensory nerves. The electrodes record the reach of the impulse to the nerves and how fast the electricity is carried.
- Muscle and nerve biopsy
Muscle biopsy is an old procedure that physicians would employ in the past for diagnosing SMA. It is still used when other diagnostic measures fail. This process involves the surgical sample removal and examination of a small muscle and nerve tissue in order to find any signs of the disorder.
Treatments for SMA
Different kinds of treatments are available for SMA affected individuals, they are as follows:
- Physical therapy
Through physical therapy, SMA patients learn certain special range-of-motion exercises that help them in keeping their muscles flexible and mobile.
Certain medications are often used to prevent damage to the cells in the central nervous system.
- Mobility aids
An electric wheelchair is often recommended by physicians for children who have type I and II SMA and are unable to stand or walk without assistance.
- Respiratory support
Respiratory support involves the use of breathing devices, yearly immunizations, supplemental oxygen, and breathing exercises.