Research into some Rarer Forms of Spinal Muscular Atrophy
Research into some Rarer Forms of Spinal Muscular Atrophy
Last reviewed and updated: 22nd January 2025
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, even rarer forms of SMA that are often collectively 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 onset1-3. 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 are known as proximal muscles), 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, which are known as distal muscles).
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 into five types of non-5q SMA:
References
1. Peeters et al. (2014) Clinical and genetic diversity of SMN1-negative proximal spinal muscular atrophies. Brain. 137: 2879–2896.
2. Fernández-Eulate et al. (2023) Phenotype Presentation and Molecular Diagnostic Yield in Non-5q Spinal Muscular Atrophy. Neurol Genet 9: e200087.
3. Zambon et al. (2023) Early onset hereditary neuronopathies: an update on non-5q motor neuron diseases. Brain 146: 806-822.