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Study of BIIB115 in patients aged 15‑60 years with spinal muscular atrophy who are treatment‑naïve or previously treated with risdiplam

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What is this trial about?

A plain-language summary of the goals, design and what participants do

The study looks at people aged 15‑60 with Spinal Muscular Atrophy, a rare muscle disease that makes it hard to move and breathe. The experimental medicine is called Salanersen (code name BIIB115), given by an injection into the fluid surrounding the spinal cord (called intrathecal injection). Some participants have never taken any SMA medicine, while others have previously used the approved drug risdiplam.

The purpose of the study is to learn whether Salanersen improves movement ability and is safe for people with this condition. Participants receive the medication at the start of the trial and then return for regular check‑ups over several months, during which doctors watch how well they can perform simple movements, walk, and use their arms. The visits also include tests that measure muscle activity and blood samples to see how much of the medicine is in the body.

Throughout the study, any side effects or health problems are recorded, and participants are asked how they feel about any changes in their condition. Simple explanations are given for each test: for example, a walking test measures the distance a person can cover in six minutes, and a motor‑function scale scores how well a person can perform 33 different movements, with higher scores meaning better ability. The overall goal is to gather information on both the benefits and safety of the treatment.

The research process

The trial runs in 7 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Baseline assessment before first dose

    You will undergo a series of tests to measure your current movement ability and muscle function. these include the hammersmith functional motor scale - expanded (hfmse), which evaluates how well you can perform 33 different movements, and the revised upper limb module (rulm), which looks at the use of your arms and hands.

    If you are able to walk, you will also complete the 6‑minute walk test (6mwt), where you walk for six minutes on a flat surface and the distance covered is recorded.

    Electrical tests called compound muscle action potential (cmap) will be performed on specific nerves to assess muscle response.

    Blood samples will be taken to check general health and to measure the level of the study drug in your serum. a sample of cerebrospinal fluid (csf) may also be collected to measure drug concentration in the fluid surrounding your spinal cord.

    You will answer questionnaires such as the patient global impression of change (pgi‑c) and the sma independence scale - upper limb module (smais‑ulm) to describe how you feel about any changes in your condition.

  2. Step 2

    First dose administration

    You will receive a single dose of biib115 (also called salanersen) at a strength of 80 mg. the medication is supplied as a solution for injection and is given by an intrathecal route, which means it is injected directly into the cerebrospinal fluid surrounding the spinal cord.

    The injection is performed by a qualified health professional in a clinical setting.

  3. Step 3

    Regular follow‑up visits

    After the first dose, you will return for scheduled visits throughout the study. at each visit you will repeat the movement tests (hfmse, rulm, and, if applicable, 6mwt) to track any changes in your ability.

    The same electrical muscle tests (cmap) and blood/csf sampling will be repeated to monitor the drug’s effect and its concentration in your body.

    Your health will be checked for any side effects. any unwanted medical problems are recorded as adverse events (aes), and serious problems are recorded as serious adverse events (saes).

  4. Step 4

    Primary efficacy assessment at month 12

    Approximately twelve months after the first dose, the main effectiveness of the drug is evaluated. the change in your hfmse score from the baseline is measured, and the overall movement score (out of a possible 66 points) is recorded.

  5. Step 5

    Extended efficacy and safety monitoring up to day 1825

    For up to day 1825 (about five years), you will continue to have the same set of assessments. these include the hfmse, rulm, 6mwt, cmap, pgi‑c, smais‑ulm, and regular blood and csf sampling.

    The study also looks for specific improvements, such as a three‑point increase in the hfmse score, a two‑point increase in the rulm score, or a 30‑meter increase in the 6mwt distance for those who can walk.

  6. Step 6

    Cerebrospinal fluid concentration monitoring up to day 1460

    Until day 1460 (about four years), additional csf samples are taken to measure how much biib115 is present in the fluid around your spinal cord.

  7. Step 7

    Final study visit and study completion

    At the end of the study period (up to day 1825), a final set of all assessments is performed. the results are used to determine the overall safety and effectiveness of biib115 for people with spinal muscular atrophy.

Who can join the trial?

12 criteria

  • Be between 15 and 60 years old when you give consent to join the study.
  • Have a confirmed genetic test showing the specific 5q Spinal Muscular Atrophy (SMA) gene change (either a deletion or mutation).
  • Show the typical signs and symptoms that doctors associate with SMA.
  • Have at least one copy of the SMN2 gene (a gene that can affect how the disease behaves).
  • Score between 10 and 54 on the Hammersmith Functional Motor Scale – Expanded (HFMSE), a test that measures motor abilities.
  • Be able to sit upright without any support for at least 10 seconds.
  • Never have used myostatin inhibitors (drugs that block a protein involved in muscle growth) and agree not to take them while in the study.
  • If you are in the treatment‑naïve group (meaning you have not received any approved SMA therapy before), you must not have taken any approved SMA disease‑modifying therapy or any experimental SMA drug.
  • If you are in the risdiplam‑treated group, you must be currently taking risdiplam at a dose of 5 mg once daily for at least 6 months before the screening visit.
  • If you are in the risdiplam‑treated group, you must be willing to stop risdiplam for the whole study period, with the last dose taken the day before the first dose of the study drug.
  • If you are in the risdiplam‑treated group, you must not have previously received nusinersen, onasemnogene abeparvovec (gene‑therapy medicines), other approved SMA disease‑modifying therapies, or any experimental SMA drugs other than risdiplam.
  • Both walking (ambulatory) and non‑walking participants can join. If you can walk, you must be able to walk at least 10 meters on your own and be able to complete the 6 Minute Walk Test (6MWT) during screening.

Who cannot join the trial?

6 criteria

  • You cannot join if you need a breathing machine (either invasive or noninvasive ventilation) for more than 6 hours in a 24‑hour period, except for a night‑time device called bilevel positive airway pressure.
  • You cannot join if a feeding tube that goes into the stomach (a gastric feeding tube) provides most of your nutrition.
  • You cannot join if you have a history of brain or spinal cord disease, severe spine curvature (scoliosis), or any condition that would make a spinal tap (lumbar puncture) or the flow of fluid around the brain and spine (cerebrospinal fluid) difficult, such as fluid buildup in the brain (hydrocephalus) or a drainage device (shunt).
  • You cannot join if you have been hospitalized for surgery, a lung problem (pulmonary event), or special nutritional support within the past 2 months, or if you plan any elective surgery or procedure from signing the consent form until the study ends. If you had scoliosis surgery, it must have been at least 1 year ago.
  • You cannot join if you have a current health issue (for example, an infection or a recent fracture) that would make participation unsafe.
  • You cannot join if you are already enrolled in, or plan to enroll in, another clinical trial that uses a new (investigational) drug or therapy within the past 90 days or within five half‑lives of that drug (the time it takes for half of the drug to leave your body), whichever is longer. This also includes treatments such as spinal cord stimulation, a type of neuromodulation therapy.
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Investigated drugs

Salanersen (BIIB115) is an experimental medicine being studied for spinal muscular atrophy (SMA). It is given as a liquid that is injected directly into the fluid around the spinal cord (intrathecal injection). The drug is designed to help the body produce more functional protein that is missing or low in people with SMA, which may improve muscle strength and overall function. In this trial, participants who have never received treatment for SMA or who have previously taken another SMA medicine called risdiplam will receive Salanersen to see how well it works and how safe it is. The study will watch for changes in the participants’ ability to move, breathe, and perform everyday activities, as well as any side effects that might occur.

What is already known about the treatment

Salanersen (BIIB115) - Salanersen is given as an intrathecal injection of a sterile solution, meaning it is delivered directly into the fluid around the spinal cord. It is currently in late‑stage clinical testing (Phase 3) and has not yet been approved for general medical use. The drug is being studied to treat spinal muscular atrophy, a rare genetic disorder that causes muscle weakness. It works by binding to the messenger RNA of the SMN2 gene and preventing a harmful splice, which increases production of the functional SMN protein; it is classified as an antisense oligonucleotide therapy.

Investigated diseases

Spinal Muscular Atrophy - Spinal Muscular Atrophy is a genetic condition that causes loss of motor neurons in the spinal cord, leading to muscle weakness. Symptoms usually appear in early childhood, but can also begin later. As the disease progresses, muscles become weaker and movement becomes more difficult, affecting activities such as crawling, standing, or walking. In some forms, the weakness spreads to the respiratory muscles, making breathing harder. The rate of progression varies between individuals, with some experiencing gradual loss of function over years while others may see faster changes.
Trial detailsLast updated 2 Oct 2026
Age18+ yearsPhasePhase IIITrial ID2025-524054-34-00Protocol code277SM303Estimated enrolment90 patientsSponsorBiogen Idec Research Limited

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