SMA – causes and symptoms. What is the treatment for spinal muscular atrophy?

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Spinal Muscular Atrophy (SMA) is a genetic disease characterized by progressive muscle wasting. It can affect both newborns and older children. What types of SMA do we distinguish? Is it possible to stop the disease completely? We check not only what the treatment looks like, but also the prognosis for patients with spinal muscular atrophy.

SMA – general characteristics

Spinal muscular atrophy is a genetically determined neuromuscular disorder. During the course of the disease, there is a complete loss of spinal cord motor neurons. The consequence of this process is weakness and progressive muscle wasting.

1. Find out how the most common genetic diseases develop

The most common form of the disease is inherited autosomal recessive childhood and juvenile spinal muscular atrophy, which leads not only to immobilization, but also to respiratory failure. Autosomal recessivity means that a child must receive one copy of the gene from both parents in order to become ill.

SMA – causes

Spinal muscular atrophy is one of the most commonly diagnosed neuromuscular diseases affecting children. The main cause of SMA is a mutation in the SMN1 gene on chromosome 5q, i.e. incorrect coding of SMN, which is a protein necessary for the proper functioning of motor neurons. The main effect of the defect is the death of the motor neurons in the spinal cord.

SMA – classification of spinal muscular atrophy

Initially, SMA was classified according to the first symptoms that appeared, but this division has been replaced by a more functional one. It is dependent on the highest level of exercise that can be achieved by a patient with spinal muscular atrophy. Therefore, the classification of SMA is as follows:

1. Type I is the early infant type also known as Werdnig-Hoffman disease – is the most severe form of the disease, affecting approx. 50% cases. The first symptoms appear early in the baby’s life, most often in the first months after birth; 
2. Type II is a late infant type – the first symptoms appear between the 6th and 18th month of the child’s life. Most often it is unable to sit by itself without a backrest. On the other hand, he may acquire this skill and it will begin to fade away; 
3. Type III is now called childhood or adolescent, but was formerly called Kugelberg-Welander disease – the symptoms appear when the child is only able to take a few steps on his own and when he has difficulty climbing stairs; 
4. Type IV also called adult – is the mildest form of SMA. Symptoms most often appear after the age of 40 or 50. The patient begins to have trouble walking. However, it should be emphasized in this context that some scientists consider the adult type of SMA to be late stage III stage.  

Type of SMA – age of onset and first symptoms

The type of SMA is differentiated based on the patient’s age and the first symptoms:

1. Type I – age of onset up to 6 months, the child is unable to sit up independently; 
2. Type II – age of onset between 6 and 18 months of age, the child is able to sit up independently, but cannot stand up alone; 
3. Type III – age of onset after 12 months of age, the child can walk without support; 
4. Type IV – age of onset over 30, the patient has difficulty walking. 

Symptoms of spinal muscular atrophy and the type of SMA

The symptoms of spinal muscular atrophy depend mainly on the type of SMA:

1. Type I – weakness of the respiratory muscles, muscles of the throat and esophagus, trunk muscles, progressive curvature of the spine, muscle laxity, difficulty lifting the head (inability to lift it up), inability to roll over, soft crying, weak cough, difficulty swallowing and suction; 
2. Type II – atrophy of the muscles closer to the torso (the thigh muscles become weaker than the calf and foot muscles, and the arm muscles weaker than the muscles of the forearms and hands), scoliosis, being able to sit down (the ability may begin to decline gradually); 
3. Type III – difficulty climbing stairs or getting up from a low armchair or from the floor, the possibility of taking single steps without support. 

Although the symptoms of spinal muscular atrophy most often depend on the type of SMA, some are common to all patients. First of all, the trembling of the fingers should be mentioned here, as well as the gradually progressive weakening of the muscle strength and the weakening or complete disappearance of deep reflexes, especially the knee reflex, which usually disappears first.

SMA diagnostics

In the diagnosis of spinal muscular atrophy, the most important thing is to conduct a genetic test, which in over 96% cases allows for a correct diagnosis by a neurologist. If SMA is suspected, electromyography and morphological examination of the muscle tissue are also performed.

Genetic screening of children and newborns for SMA can be done at Medonet Market. A self-blood collection kit is sent to the person who has decided to redeem the offer. The genetic material is then sent to the laboratory, and the results are available for collection within 1-2 weeks.

Prenatal tests and SMA diagnostics

Spinal muscular atrophy can be diagnosed in a fetus that is several weeks old. There are two options for prenatal testing, chorionic villus sampling and amniocentesis. The first one involves taking a slice of genetic material from the fetus with a long needle. Amniocentesis allows the collection of amniotic fluid.

1. What is prenatal testing?

Both methods carry a risk of miscarriage, but it is estimated at 1%. If both parents are carriers of the SMN1 gene, and at the same time want to rule out the disease in their child, they may decide to undergo in vitro fertilization.

Treatment of SMA

Treatment of SMA depends primarily on the type of spinal muscular atrophy. Its main goal is to improve the quality of life of patients. The patient should be under the constant care of a neurologist, dietitian and pulmonologist.

In addition, the comfort of life is definitely influenced by rehabilitation, not only in professional centers, but also at home. In the treatment of SMA, the following are mainly used:

1. Gene therapy – it consists in an attempt to influence the SMN1 gene by viruses containing missing fragments of damaged DNA; 
2. Taking medicines protecting motor neurons against protein loss; 
3. exoskeleton – it was presented for the first time in 2016. It can be used in patients between 3 and 14 years of age, because it has adjustable elements that adapt to the length of the limbs. Wearing the exoskeleton prevents the lateral curvature of the spine from getting worse. 

SMA prognosis

The prognosis for patients with spinal muscular atrophy is very difficult to determine due to the individual patient’s abilities and the type of care the patient is provided with.

Drugs and SMA – the most expensive in the world?

Pharmacological treatment is very often used to improve the patient’s quality of life, as well as to slow down or inhibit the symptoms.

One of the most popular and at the same time considered one of the most expensive drugs in the world is Spinraza (Nusinresen) taken for an indefinite period of time. Dosing consists of four loading doses – three at two-week intervals and a fourth taken 4 weeks after the third, and a maintenance dose that is given to the patient every four months.

Another drug is Risdiplam taken once a day by gavage or peg, or by mouth. Currently, the drug can only be purchased in the United States, but from August 2020 it can be used outside the US in severe cases of the disease. Talks are also underway to introduce Risdiplam to the European Union.

In addition to Spinraza and Risdiplam, experimental drugs such as Branaplam, Reldesemtiv and SRK-015 can also be used in the treatment of spinal muscular atrophy.

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