Spinal Muscular Atrophy (SMA)

(SMA Type-1 / SMA Type-2/ SMA Type-3 / SMA Type-4)

Introduction
SMA is a group of neuromuscular disorders where there is substantial muscles weakness and muscles wasting. These are progressive in nature. The proximal muscles are affected before the distal muscles. 

Prevalence / Incidence of SMA
Nearly 1 in 11,000 live birth

Signs / Symptoms of SMA
Mostly children with SMA will have

• Hypotonia or low muscle tone
• Fasciculation-Involuntary contractions or twitching of muscles
• Absent or decreased DTR ( Deep Tendon Reflexes)
• Respiratory Problems
• Feeding problems, etc

Type of SMA
Four types of SMA have been reported. These are
SMA Type 1 is the most severe form of SMA. It is also called “Werdnig-Hoffmann disease”. Children with SMA type 1 are floppy, can’t sit without support, and have trouble breathing, feeding and swallowing. Symptoms begin within first few months after birth. Most children with SMA type 1 do not live more than 2 years of age.

SMA Type 2 is an intermediate form of SMA. Children with SMA type 2 can sit without support at some point but are unable to walk independently. Symptoms can be seen between 6 and 18 months of age. Depending on the severity of the symptoms, mostly children with SMA type 2 have a normal life span.

SMA Type 3 is a milder form of SMA. It is also called as “Kugelberg-Welander disease”. Most of the children with SMA type 3 are able to walk independently, may have some walking difficulty. A few may need the support of a wheelchair in late adulthood. Symptoms can be seen approximately at 18 months of age. Children with SMA Type 3 generally have nearly normal life expectancy.

SMA Type 4 is very rare. It generally appears in young adulthood, and causes very mild motor deficit.

Causes of SMA
Spinal muscular atrophy is generally due to a genetic mutation in the SMN1 gene
Associated factors with SMA
Children with SMA have a number of associated / co-morbid conditions which need extra attention and specialized treatment. These problems are

• Respiratory Problems
• Feeding and nutritional issues
• Scoliosis- A spinal deformity
• Hip dislocation- A hip deformity
• Behavior issues
• Sleep disorders, etc

Diagnosis making of SMA
Diagnosis of SMA is confirmed with the help of molecular genetic testing. Molecular genetic testing is a specialized test which is done to determine if a mutation is present in the SMN1 gene. It can also be used to determine the number of copies of the SMN2 gene. Before going for molecular genetic testing, primarily EMG/ NCV and CPK are done.

Treatment / Management of SMA
Just after the diagnosis is made, the infant / child are referred to a specialized habilitation team / centre for medications and therapies. Newer medicines are prescribed by a pediatric neurologist if there is mutual agreement between the parents and the treating physician.

Developmental therapy (combination of physiotherapy and occupational therapy) is started as soon as possible to stimulate the infant / child to achieve milestones and muscular strength. Need based postural aids, orthoses and mobility aids are prescribed time to time.

All associated problems are taken care simultaneously by other specialists.

During the last 10 years, a few newer medicines have come up. These medicines are very costly so the use of medicines is very selective and limited  
The following medicines have been used to treat SMA worldwide

• Nusinersen / Spinraza is administered directly to the CNS using an Intrathecal injection
• Olesoxime, a neuroprotective drug help in retaining the motor neurons
• CK-2127107 is a skeletal troponin activator helps to counter the effect of SMA

Use of Stem Cell to treat SMA
Lots of organization has been treating SMA through stem cell therapy but there is no supportive evidence available

Gene Therapy and SMA
The US FDA has approved the first gene therapy to treat children less than two years of age with SMA. SMA gene therapy in a few clinical trials have shown clear efficacy in young children with SMA type 1. Improvements has been observed in gaining motor skills and decreased need for respiratory support
Zolgensma, a form of gene therapy is prescribed to treat children less than 2 years with SMA

Prognosis and outlook of SMA
The prognosis depends on the kind of SMA.

SMA Type-1
Most children with SMA type 1 do not live more than 2 years of age.

SMA Type-2
Depending on the severity of the symptoms, mostly children with SMA type 2 have a normal life span.

SMA Type-3
Children with SMA Type 3 generally have nearly normal life expectancy.

SMA Type-4
It causes very mild problem. There is no such problem with life expectancy

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