Topic: Research Status of Spinal Muscular Atrophy

Less than ten years ago spinal muscular atrophy (SMA) was the leading genetic cause of child mortality and a difficult diagnosis to share with patients and their families. By combining the power of molecular genetics and modern drug discovery approaches, the prognosis for patients with SMA in 2023 is much improved. There are now three approved therapies driving the restoration of the survival motor neuron (SMN) levels. SMA is a neuromuscular disease associated with the loss of motor neurons and muscle atrophy due to low levels of SMN resulting from inactivating mutations in the encoding gene SMN1. The SMN2 gene is present in varying copy numbers in individuals, and due to a single nucleotide change in exon 7 from SNM1 it cannot sustain productive splicing of its pre-mRNA. As a result of this single difference, much less protein is produced from the SMN2 gene than the SMN1 gene. The more copies of the SMN2 gene, the less severe the disease. 

Two of the SMN restoration therapies (SPINRAZA® (nusinersen) and Evrysdi® (risdiplam)) act on the SMN2 gene, to modulate the splicing of SMN2 so as to incorporate exon 7 into the mRNA and produce full-length SMN protein. The third SMN restoration therapy is an AAV9-SMN gene therapy (ZOLGENSMA® (onasemnogene abeparvovec-xioi)). Despite the introduction of these breakthrough therapies, there remains significant medical need with two major areas of focus – regenerative medicine approaches aiming to restore loss of function prior to the start of therapy and understanding the biology of SMA beyond SMN protein restoration.

Development of therapies for SMA has been greatly facilitated by a clear understanding of the molecular basis of the disease including the role of SMN protein and the pathology elicited by the reduced, hypophysiological levels of SMN protein. 

The goal of this Special Issue is to provide the current assessment of new targets, therapeutics, and strategies for the treatment of SMA as well as new research that will give further insight into the pathology of the disease. 

We welcome Original Research Articles, Review Articles, and Brief Communications. This might include:

- Status of SMA disease post-SMN restoration therapy, are patients ‘cured’ or is there much work still to be done?

- Regenerative approaches for therapy post-SMN restoration focused on motor neurons, muscle, and neuromuscular junction; the role of trophic factors in SMA;

- Animal models of SMA and translational studies;

- Biomarkers - predictive and pharmacodynamic;

- The role of SMN in prenatal development and therapeutic approaches that may be envisioned to address SMN deficiency before birth;

- Also of interest are reviews of neuromuscular disease (NMD) space and the lessons from SMA therapy development may be used to guide drug discovery and development in other NMD indications;

- Current understanding and working hypotheses why motor neurons are most vulnerable to reduced SMN protein levels; 

-SMN expression is ubiquitous – what mechanisms for pathology are cell autonomous, peripheral, and/or central.

We welcome manuscripts covering both preclinical and clinical studies.