Spinal muscular atrophy is a disabling medical condition mostly detected in children. The voluntary muscles become weak, and kids are unable to control their movements. Usually, the muscles near the center of the body like the shoulders, hip, and thighs get impacted at first. If the condition is not detected in the early stages and immediate disease-modifying therapies (DMTs) are not initiated, then the situation can turn fatal.

The causes of spinal muscle atrophy
It is crucial to know the following causes of spinal muscular atrophy to have a better understanding of this inherited progressive neurodegenerative disorder.

Genetic causes
Genetic factors are one of the most significant causes of spinal muscle atrophy .  The SMN1 and SMN2 genes present on the human chromosomes remain concerned with the production of SMN (survival of motor neuron) proteins. In healthy individuals, this protein controls the transmission of impulses from the brain and the spinal cord to skeletal muscles, signaling them to move. Though the SMN protein is present throughout the system, they have the highest concentration on the brainstem.

In spinal muscular atrophy patients, there is a defect in the expression of SMN1 and SMN2 genes. Studies have proved that homozygous mutations in the SMN1 gene on chromosome 5 can lead to this autosomal recessive disease in 94 percent cases. In this type of mutation, the fetus inherits defective genes of the same pattern from both parents. The SMN1 gene plays a pivotal role in the expression of SMN proteins, whereas SMN2 genes can guide its synthesis only to a small amount. So, if the SMN2 genes perform correctly in SMN1 mutated individuals, then it can make up to some extent the deficiencies of SMN1 coding.

Structural causes
The structural causes of spinal muscle atrophy also play a decisive factor in the expression of the genetic disorder. Since SMA patients have insufficient SMN protein in the body, they form weak motor neurons. These nerve cells are unable to receive and transmit impulses. Hence, they fail to co-ordinate the movement of skeletal muscles. As the disease progresses, the voluntary muscles continue to receive feeble impulses from the brain. Over a while, they shrink in size and show atrophy. However, the involuntary muscles concerned with the peristalsis, bowel, and lungs movement do not get affected. So, the vital functions of the body go on without many challenges.

Rare genetic causes
In some unusual cases, two other genes- DYNC1H1 (cytoplasmic dynein 1 heavy chain 1) and UBA1 (Ubiquitin-like modifier activating enzyme) may also cause spinal muscular atrophy. A mutation of DYNC1H1 present on chromosome 14, inherited through an autosomal dominant pattern, can also lead to SMA.

Besides the above causes of spinal muscle atrophy ,  remember that parents with a family history (carriers) have 25 percent more chances of transmitting the genetic disorder to their progenies. So, it is better to conduct a genetic analysis when you are planning to start a family.