Page last reviewed and updated: December 2022

SMA is a rare condition. For most individuals (over 95%), it is caused by a fault in the ‘q’ region of chromosome 5 and is therefore known as “5q SMA”. This includes SMA Types 1-4. However, there are additional, rarer forms of SMA that are often referred to as “non-5q SMA”.

There are about 20 different genes currently linked to non-5q SMA, which can have varying symptoms, severities and ages of onset¹. Non-5q SMA can be broadly sub-categorised as either proximal SMA or distal SMA. People affected by a proximal form of SMA tend to display more pronounced weakness in the muscles closest to the body (e.g., those used for breathing and maintaining posture), which is similar to 5q SMA. In contrast, distal SMA affects the muscles further away from the body (e.g., those found in the hands and feet).

Because non-5q forms of SMA are usually very rare, there is often a long delay before a diagnosis is made and, due to the small numbers of individuals affected by these conditions, research is severely limited.

This summary gives information on and links to research that has been carried out in three types of non-5q SMA:

• Kennedy’s disease >
• SMARD >
• Distal SMA-V (GARS1) >

No drug treatments have so far been approved for any non-5q SMA, so clinical care and appropriate management remain the focus for optimising quality of life.

References

1. Peeters et al. (2014) Clinical and genetic diversity of SMN1-negative proximal spinal muscular atrophies. Brain. 137: 2879–2896.