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SMA is caused by mutation of the SMN1 gene. Researchers think that we may be able to treat SMA by replacing this faulty gene.

A type of treatment known as gene therapy, or gene transfer, is thought to be a viable option for restoring the SMN protein that is lacking in people with SMA. As well as replacing SMN1, gene transfer, targeting other important genes, could also be used to provide additional protection to motor neurons, the main cells affected by SMA.

Gene therapy uses short pieces of DNA from genes, for example SMN1 for SMA. As it is not possible to insert the gene directly into a cell, scientists use a carrier called a vector to deliver the gene to the human cells that need it. For human gene therapy, harmless viruses are the vectors used to ‘infect’ the cells with the new DNA. Importantly, the viruses are modified so that they are not contagious and cannot cause disease.

The main cells affected by SMA, the lower motor neurons, are found in the spinal cord. This means vectors have to cross the blood-brain barrier in order to reach these target cells. The blood-brain-barrier is a semi-permeable covering that protects the brain from foreign substances and maintains a constant brain environment. Finding gene transfer techniques that can cross this barrier presents a real challenge.

During this time there were phenomenal developments. From 2022 onwards, updates about clinical trials and treatments using this approach are tracked in the pages about any specific treatments being investigated.


18th January: Study showed Zolgensma can benefit children previously treated with nusinersen – read more.


17th August: Phase 3 of the Zolgensma STEER trial announced.

23rd April: Global trial of the SMART trial to investigate the safety, tolerability and efficacy of intravenous Zolgensma™ in children who have SMA and weigh between 8.5 kgs and 21 kgs announced.

8th March: Zolgensma accepted for restricted use in Scotland

8th March: NICE and NHS England announced restricted access in England.


3rd July: European Clinical Consensus on ad hoc use of Zolgensma published.

19th May: European Commission approved Zolgensma.

27th March: Avexis published trial data from SPRINT, STRIVE-US and START showing Zolgensma shows rapid significant and clinically meaningful therapeutic benefit to patients.

19th March: Zolgensma approved in Japan.


30th October: Intrathecal trials put on hold in the US.

24th May: Zolgensma approved for use for children aged less than 2 years in the US.


6th December: US Food and Drug Administration (FDA) accepted Zolgensma for review with Priority Status.

3rd May: Novartis agrees $8.7 billion deal to acquire Avexis


15th December: Avexis announced Phase 1 of STRONG trial for intrathecal administration of Zolgensma to children who have SMA Type 2.

5th April: Avexis announced results from the START trial.


28th July: AVXS-101 receives “Breakthrough Therapy” status in the USA.

23rd May: Previously known as scAAV9.CB.SMN and ChariSMA™, the latest reported data of AVXS-101 drug showed that it continued to appear safe and well tolerated by the young SMA patients in the trial.


March: Professor Burghes published study of SMN Gene Therapy in a large animal SMA Model.


30th April: Avexis announces SMN1 Gene Therapy trial in the USA.

8th October: ChariSMA™, a potential gene therapy program for SMA, received Orphan Drug Designation

12th – 14th June: Dr James Sleigh, SMA UK’s Scientific Research Correspondent attended the annual Cure SMA Conference in the US and provided a summary report of the presentations and discussions about The Importance of Delivery for SMN Gene Therapy.

15th April: ReGenX Biosciences, LLC and AveXis, Inc. agreed to an exclusive license for the development of gene therapies to treat SMA using viruses known as NAV® rAAV9 vectors. Previously known as scAAV9.CB.SMN, AveXis christened the experimental drug ChariSMA™.

At the same time Phase 1 of the START trial in the US was announced.


23rd October: Gene therapy, scAAV9.CB.SMN received fast track status in the US.

12th February: The Azzouz Laboratory published a report on gene therapy for SMA


Our Scientific Research Correspondent, Dr James Sleigh, collated reports from published studies from the laboratories of Dr. Brian Kaspar, Dr. Martine Barkats, and Prof. Mimoun Azzouz. These showed that the adeno-associated virus type 9 (AAV9) is able to cross the blood-brain barrier and produce SMN protein, resulting in drastic improvements in SMA model mice.