Multiple diseases and disorders affect the muscle functioning, either directly by impairing the voluntary muscles or indirectly by affecting the nerves or neuromuscular junction supplying the muscles. All these are grouped under neuromuscular disorders. Spinal muscular atrophy or SMA belongs to this neuromuscular disorder group and involves continuous muscular wasting and loss of the motor neurons of the body. Spinal muscular atrophy or SMA can be fatal in nature.
Classifications of SMA Disease
Depending on the severity of the protein deficiency and onset of symptoms, the spinal muscular atrophy is characterized into 4 types: Type 1, Type 2, Type 3 and Type 4.
SMA Type 1 Disease:
The SMN1 gene mutation leads to abnormal proteins and the symptoms are present from the time of birth of a child or if the symptoms appear by the age of 6 month, it is classified into SMA type 1.
SMA Type 2 Disease:
Spinal Multiple Atrophy occurring in children of age between 7 months to one and a half year of age is termed as Type 2 Spinal muscular atrophy. These children affected with SMA type 2 are seen to have a minimum of 3 SMN gene 2 in their chromosomes. This group of children is unable to walk independently. SMA type 2 is also termed as intermediate spinal muscular atrophy.
SMA Type 3 Disease:
The SMA affecting the children more than 18 months of age is classified under type 3. This group of children can walk and stand on their own.
SMA Type 4 Disease:
SMA Type 4 is known to involve adult age group. It is also called as adult- onset SMA or Kugelberg-Welander disease.
People suffering from SMA Type 3 and type 4 have at least four to nine SMN2 genes in their chromosomes.
What is SMA Type 1 Disease?
SMA type 1 disease is a condition when there is a genetic mutation in SMN 1 gene leading to abnormal secretion of proteins from birth and the symptoms onset before the age of 6 months. This is also termed as infantile onset because of its early onset of symptoms or Werdnig-Hoffmann disease. These babies have only two SMN gene 2 present in their chromosomes.
Symptoms of SMA Type 1 Disease
The symptoms of SMA type 1 disease include:
- Muscular weakness
- Frequent falls and increased tendency to flop
- Poor muscle tonicity
- Difficulty in breathing
- Weak respiratory muscles causing weak cry and cough
- Recurrent respiratory infections
- Difficulty in swallowing
- Babies have difficulty in sucking milk
- Tongue twitching
- Slow growth and development activity
- Babies are unable to sit on their own and need assistance
- Difficulty in learning to stand
- Slow or impaired reflexes of the extremities.
Causes of SMA Type 1 Disease
Spinal Multiple Atrophy is known to occur by deficiency of a protein called SMN (Survival of motor neuron) protein. SMN gene 1 is present in both the pair of chromosome 5 in human body. The mutation of this gene leads to production of functional SMN proteins which are of smaller size and are not full length. Another neighboring gene known as SMN 2 gene is present in the chromosomes which produce the proteins similar to SMN 1 gene, but these proteins are not functional and are shorter in size as compared to the SMN proteins by gene 1. However, some SMN proteins produced by SMN2 genes are full length as well as functional in nature. Hence these can compensate for the SMN1 gene protein deficiency.
Prognosis of SMA Type 1 Disease
It is observed that most of children suffering with SMA type 1 do not progress to SMA type 4 levels. However, with appropriate care, the type 1 SMA that is mild in nature can survive till adulthood. The progression of SMA type 1 disease is low. The severe cases have shown less life expectancy; however, the treatment to improve the respiratory distress with advanced management has lowered the mortality rate in children with SMA type 1.
Treatment of SMA Type 1 Disease
The management of SMA or spinal muscular atrophy depends on the severity of the disorder. The management includes:
Since it is seen that respiratory system is the most affected system in SMA type 1 disease, it is important to manage the respiratory muscles. The ways would include:
- Manual clearance of secretions or chest physiotherapy is beneficial for postural drainage.
- Use of mechanical cough assistance device is helpful.
- In severe cases, non-invasive ventilation and tracheostomy can be performed.
- Difficulty in swallowing and sucking can lead to nutritional deficiency and nutrition related disorders in babies. Feeding tube and gastrotomy can be performed to help the child to provide proper nutrition to avoid any nutrient deficiency.
- Adults are advised to avoid prolonged fasting and take a low-fat diet to avoid organic acidemia due to beta oxidation of fatty acids in muscles. Also, soft food intake is not recommended to avoid aspiration.
Exercise and Physical Activity for SMA Type 1 Disease:
Since SMA is related to muscle weakness, an assisted physiotherapy is beneficial to prevent any structural developmental disorders like kyphosis, scoliosis, etc. To help achieve proper gait, Orthotic devices can be used.
Medications for SMA Type 1 Disease:
Nusinersen, also called as Spinraza, is the medicine used to treat the spinal muscular weakness and is approved by the regulatory authority. It is administered by intrathecal injection to act over the central nervous system directly.