Spinal muscular atrophy (SMA) refers to a set of genetic disorders wherein an individual has no control over their muscle movement, because of nerve cell damage or loss in the brain stem and spinal cord. It’s a type of motor neuron disease that affects 1 in 8 people worldwide.
SMA causes difficulties in normal body movements like standing, walking, and even in breathing and swallowing. It cannot be cured, but its progression can be slowed down with the help of medicinal drugs.
Spinal muscular atrophy is a disease responsible for muscle wasting weakness, and may have a significant effect on life expectancy. In some cases, SMA could be congenital, but commonly, it appears later in life.
Types of SMA
According to The National Institute of Neurological Disorders and Stroke, SMA can be classified into four types as follows:
SMA Type-I
This is also called the Werdnig-Hoffmann Disease. The condition may appear even in six month old babies. The child may be born with breathing problems, and without treatment, it can turn fatal within one year.
Symptoms:
- Muscular weakness
- Twitching
- Poor limb movement
- Problems in feeding
- Curved spine (over time)
Certain tests may reveal SMA Type 1 in the unborn babies a– especially those with low fetal movements in the final months of pregnancy as seen in the scan. Otherwise, it is detected when the baby is just a few months old.
New treatments like disease modifying therapies or DMTs are now available that can help some children with SMA Type 1 to sit, stand or walk.
SMA Type-2
Symptoms of this disease are observed in the 6 to 18-month period. Some affected children may be able to sit. But in many cases, they may never be able to stand or walk. Some cases are so severe that without treatment, the patient’s ability to even sit is lost.
Life expectance is dependent on the presence of breathing problems. Most children with SMA Type-2 survive long enough to become young adults, or at least to adolescence.
SMA Type-3
Also called the Kugelberg-Welander Disease, SMA Type-3 makes its appearance after 18 months of age in new born babies. The child may have shortened muscles or tendons – scoliosis or contractures. This disease hinders free movement of the joints.
People are normally able to walk, albeit with an odd gait. They are likely to find it difficult to run, get up from a chair, take stairs, and experience tremor in their hands. Patients of SMA Type-3 are more susceptible to respiratory infections. In these cases, DMT and other treatments can enable the patient to have a normal life expectancy.
Adult SMA
The Type-4 SMA is quite rare. It begins after the person turns 21. The muscles closest to the center of the body center are the ones most affected – this is called proximal weakness, and can range from mild to severe. Life expectancy is not impacted by this type of spinal muscular atrophy.
Symptoms of SMA
Though the symptoms are varied depending on the type and severity of the condition, and the age at which it manifests, there are some common symptoms that include:
- Weakness in the muscles
- Twitching muscles
- Difficulty in breathing and swallowing
- Difficulty in sitting, standing, walking, climbing, and running
- Unusual shape of limbs, chest, and spine caused by weak muscles
Those born with SMA Type-1 have weakened muscles, minimal muscle tone, and problems in breathing and feeding.
SMA Type-3 usually manifests only in the second year of life.
Muscle weakness and wasting are the main features of spinal muscular atrophy. This happens because the motor neurons fail to signal the muscles to contract. The muscles closest to the center of the body are the most affected by this nerve failure. Being a degenerative disease, the symptoms of SMA get progressively worse over time. The therapy is partially useful in mitigating the problems arising with muscle weakness.
Causes
Spinal muscular atrophy occurs when motor neurons (nerve cells that control movement) situated in the brain stem and spinal cord don’t function at all, or stop functioning because of changes in genes called survival motor neuron 1 and 2, also called SMN1 and SMN2. These are the genes that direct the creation of proteins necessary for the working of motor neurons.
Dysfunction of SMN1 causes SMA; any issues with SMN2 will determine the type as well as the severity of the SMA.
Risk Factors
If both parents have a problem with the SMN1 gene, there is a 1 in 4 chance that the child will inherit it too and have SMA. 1 in 40-60 adults have genetic problems that can cause SMA.
Diagnosis
Diagnosis is begun when a child’s caregivers begin to observe symptoms of SMA in a child. Your doctor will take down a detailed medical history of the patient and family, and conduct a physical examination. The doctor will need to check if the muscles are floppy, and check the deep tendon reflexes, twitching, and so on.
Tests may include:
- Blood tests
- Muscle biopsy
- Genetic tests amniocentesis or chorionic villus sampling during gestation – helps to evaluate the unborn fetus
- Electromyography(EMG) – evaluates muscle, nerve cell, and motor neuron health and condition
Routine genetic screening for SMA as soon as a baby is born may help early detection and treatment to prevent the onset of symptoms, or minimize them.
Treatment
Spinal muscular atrophy cannot be cured or prevented – as it is a hereditary condition. There are, however, treatments that can improve the quality of live and reduce the impact of the disease on certain patients.
Medications
Currently the FDA has approved these two drugs:
Spinraza
This is used to treat all types of SMA. Your doctor will administer 4 doses first in a span of 2 months followed up by a maintenance dose, once in 4 months. Spiranza is an antisense oligonucleotide (ASO), which tries to resolve the problem by influencing the production of RNA. It can help reduce muscle weakness and slow the progression of SMA, but the degree of effectiveness varies from patient to patient.
Zolgensma
Administered by doctor, this single dose infusion medicine is a type of gene therapy that is used to treat infants less than 2 years old. Researchers are working on gene replacement therapy, stem cells for replacing damaged motor neurons, and other treatment options.
Researchers are working on other treatment options, such as gene replacement therapy and the use of stem cells to replace damaged motor neurons.
Assistive devices and therapy
- Physical therapy like water-based exercises, wheelchair sports for strength improvement.
- Assistive technology including ventilator, powered wheelchairs, modified access to computers etc. allow patients with SMA to have better quality of life
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