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Risdiplam (RG7916, RO7034067) is a new oral medication for SMA currently under development. Risdiplam modifies the SMN2 gene in such a way that the gene begins to produce increase amounts of SMN protein.

Risdiplam is being developed by a consortium composed of SMA Foundation, a US nonprofit organisation which has funded much of preclinical work; PTC Pharmaceuticals, a biotechnology company that has developed the molecule; and Roche, one of the biggest pharmaceutical companies in the world.

Risdiplam is a successor to RG7800, an earlier molecule that was trialled in patients in a study called MOONFISH. The development of RG7800 was stopped in 2015 at Phase 2 after unexpected toxicity was observed in laboratory animals (although not in participating people).

In January 2020, Roche made risdiplam available globally through a Pre-Approval Access/Compassionate Use Programme.

Clinical trials

Risdiplam was tested for safety in healthy adult volunteers in early 2016. After finding no safety concerns, phase 2/3 clinical trials started in late 2016, this time involving actual SMA patients. As of now, the compound’s properties are being tested in four trials:

  1. FIREFISH – a clinical trial that has enrolled 48 babies diagnosed with SMA type 1 aged 1–7 months. This is a 24-month open-label trial where all children receive risdiplam (there is no placebo). The trial consists of two parts. The Part I tested the drug’s biological activity and safety in two different dosing regimens. The ongoing Part II measures the compound’s efficacy at the optimal dose selected in Part I. Recruitment was completed in late 2018, and as of October 2019, FIREFISH is ongoing in Belgium, Brazil, China, France, Germany, Italy, Japan, Poland, Russia, Spain, Switzerland, Turkey and the United States. Final results are expected in late 2020 or early 2021.
  2. SUNFISH – a clinical trial for children, teenagers and young adults aged 2–25 who have SMA type 2 or 3 and are unable to walk unsupported. Like FIREFISH, this is a 24-month trial that consists of two parts: Part I, which designed to find out the optimal dose, and Part II, which aims to verify the molecule’s efficacy. Unlike the FIREFISH trial, SUNFISH is a controlled trial in which 67% participants receive the active substance and 33% receive placebo for some time. After the controlled stage (12 months in Part II), all the participants in the placebo group are switched to risdiplam. Recruitment for SUNFISH closed globally in July 2018; no UK hospital is participating.
  3. JEWELFISH – a clinical trial for people with SMA aged 12–60 who had earlier received RG7800, olseoxime, or nusinersen (Spinraza). As of October 2019, the trial has started in several countries, including the UK, and has encouraging preliminary results.
  4. RAINBOWFISH – a clinical trial for babies younger than 6 weeks who have been diagnosed with SMA but do not yet show symptoms. All babies will receive risdiplam for 24 months and then invited to take part in a 3-year extension trial. As of October 2019, the trial is ready to accept patients in several sites across the world (but none in the UK).

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