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What Is Spinal Muscular Atrophy?

Medikoe Health Expert

Medikoe Health Expert

  Koramangala, bengaluru, karnataka, india, Bengaluru     Feb 9, 2017

   2 min     


It is a genetic disease affecting the part of the nervous system that controls voluntary movement. Most of the nerve cells that control muscles are located in the spinal cord, which accounts for the word spinal in the name of the disease. It is a muscular disease because its primary effect is on muscles, which do not receive signals from these nerve cells. Atrophy is the medical term for getting smaller, which is what generally happens to muscles when they are not active.

Types of SMA

There are four types of SMA, categorized by the disease’s severity and the age at which symptoms begin:

Type I: It begins to affect infants from birth up to 6 months of age, with most babies showing signs of the disease by 3 months. It is also called as Werdnig-Hoffmann disease.

Type II: it begins to affect children between 6 to 18 months old. It is also called chronic infantile SMA.

Type III: It begins to affect kids as early as 18 months of age or as late as adolescence. It is also called Kugelberg-Welander disease.

Type IV: People affected by this type start having symptoms after age 35, and these symptoms slowly get worse over time. It develops slowly, so it is difficult to recognize its symptoms.


Chromosome 5 SMA is caused by a deficiency of a motor neuron protein called SMN, for the survival of motor neuron. This protein is necessary for normal motor neuron function. Its deficiency is caused by genetic flaws on chromosome 5 in a gene called SMN1. Neighbouring SMN2 genes can in part compensate for non-functional SMN1 genes.


The primary symptom is the weakness of the voluntary muscles. The muscles most affected are those closest to the centre of the body, such as shoulders, hips, thighs, and upper back muscles. If the muscles of the back weaken, spinal curvatures can develop.


A doctor might realize that child has SMA only after the child misses certain developmental milestones, such as being able to support his or her head or stand without help.

Test to diagnose SMA are:

  • Electromyogram (EMG)
  • CT scan
  • MRI
  • Muscle tissue biopsy
  • Blood test to look for SMN1 gene


There is no cure for SMA. The treatment for SMA varies, depending on their age and the severity of symptoms. Children with SMA usually require ongoing care throughout their lives from many different types of doctors, including pulmonologists, neurologists, orthopaedist and orthopaedic surgeons, gastroenterologists, nutritionists, and physical and occupational therapists.

Tags:  nervous system,

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