Diana Castro, MD, founder of the Neurology Rare Disease Center in Dallas, Texas discusses the most common early symptoms observed in the different types of spinal muscular atrophy (SMA).

SMA is a genetic disease that affects motor neurons in the spinal cord and control of muscle movement. It is caused by a mutation in the survival motor neuron gene 1 (SMN1) which affects nerve cells and leads to loss of muscle function. The codes for the SMN protein that appears to play a role in regulating small nuclear ribonucleoproteins complexes. Lack of that protein leads to cellular imbalances that in turn causes the motor neuron endplates to not properly connect to muscle and the motor neurons die.

Recently, the JEWELFISH study evaluated the safety, pharmacodynamics and exploratory efficacy of risdiplam in previously treated patients with Types 1-3 SMA aged 6 months to 60 years and previously treated with other SMA-targeting therapies. New exploratory data from the study showed improvement or maintenance of motor function after two years of treatment, as wells as a sustained increase in SMN protein levels.

There are several types of SMA based on age of onset and the manifestation of the disease. Type 0 SMA begins prenatally while those with type 1 start to show symptoms at birth or soon thereafter.  Type II, diagnosed in children between the ages of 6 months and 2 years, results in a delay or failure to reach motor milestones. Children with Type III, usually diagnosed before age 3 and sometimes as late as their teenage years, learn to walk but have mobility problems as they grow. Other forms of SMA that are caused by mutations in genes other than SMN1 are spinal muscular atrophy respiratory distress (SMARD), distal SMA, and Kennedy’s disease.

SMA is a progressive disorder. Therefore, the sooner a person with SMA can be diagnosed and be given proper treatment, the better the chances they have of maintaining a certain level of activity and quality of life. 

Once a person has been diagnosed with SMA—often by newborn screening—there are several  approved treatments available to delay (nusinersen, risdiplam) or possibly stop (onasemnogene abeparvovec) disease progression. 

For more information about SMA and other rare neuromuscular disorders, visit checkrare.com/diseases/musculoskeletal-diseases