The sponsors, Biogen and Ionis Pharmaceuticals, designed the trial in collaboration with clinicians who had experience in the treatment of spinal muscular atrophy. An independent data and safety monitoring board provided trial oversight in collaboration with the sponsors. Investigators collected the data, which was analyzed by the sponsors. All the authors contributed to data interpretation and manuscript development, approved the manuscript for submission, and vouch for the accuracy and completeness of the reported data. All the principal investigators agreed to follow the protocol and protocol amendments (available with the full text of this article at NEJM.org). The first draft of the manuscript was written by the first author and the senior industry author (penultimate author); medical-writing assistance was paid for by Biogen. The sponsors reviewed the manuscript and provided feedback to the authors, who had full editorial control.
Infants at 31 centers were enrolled in the trial. Eligible infants had genetic documentation of a homozygous deletion or mutation in the SMN1 gene. They also had two copies of the SMN2 gene, had had onset of clinical symptoms that were consistent with spinal muscular atrophy at 6 months of age or younger, were 7 months of age or younger at screening, did not have low peripheral oxygen saturation, and met all additional eligibility criteria (see the Supplementary Appendix, available at NEJM.org). A health care proxy for each patient provided written informed consent. The trial was approved by an ethics committee at each institution and was conducted in accordance with the International Conference on Harmonisation guidelines for Good Clinical Practice and with the World Medical Association Declaration of Helsinki.
Trial Design and Treatment
After a screening period of up to 21 days, eligible infants were randomly assigned, in a 2:1 ratio, to undergo intrathecal administration of nusinersen (nusinersen group) or a sham procedure (control group). The nusinersen dose was adjusted according to the estimated volume of cerebrospinal fluid for the infant’s age on the day of dosing, such that the infant received a dose that was equivalent to a 12-mg dose in a person 2 years of age or older; thus, younger infants were injected with smaller volumes that contained lower doses of the drug. To maintain blinding, nusinersen was administered or the sham procedure was performed by dedicated trial personnel who were aware of the group assignments, whereas the infant’s parents and key trial personnel who were responsible for assessments were unaware of the group assignments and were not present for the procedure. The sham procedure consisted of a small needle prick to the skin over the lumbar spine, which was covered with a bandage to simulate the appearance of a lumbar-puncture injection. Randomization was stratified according to disease duration at screening, which was the age at screening minus the age at symptom onset (≤12 weeks or >12 weeks).
Trial Procedures and Outcomes
In the nusinersen group, doses were administered on days 1, 15, 29, and 64 and maintenance doses on days 183 and 302. In the control group, sham procedures were performed on the same days. Efficacy end points were assessed on days 64, 183, 302, and 394 (±7 days for each visit). Safety-monitoring visits occurred on days 16, 30, 65, 184, and 303. Follow-up after the procedure consisted of weekly assessments by telephone and a visit to the study center on day 394 (±7 days). A prespecified interim analysis was performed by the sponsor and the data and safety monitoring board when approximately 80 infants had been enrolled for at least 6 months (Fig. S1 in the Supplementary Appendix). The analysis showed a benefit–risk assessment in favor of nusinersen. This result prompted early termination of the trial. At that time, infants were invited to complete an end-of-trial visit at least 2 weeks after they had received their most recent dose of nusinersen or undergone their most recent sham procedure. The assessments that were scheduled to be performed on day 394 were performed at the end-of-trial visit. Infants who completed the ENDEAR trial were invited to enroll in the open-label extension study SHINE (ClinicalTrials.gov number, NCT02594124).
The trial had two primary efficacy end points. The first was a motor-milestone response, which was defined according to results on the Hammersmith Infant Neurological Examination (HINE). The HINE is a three-section, 37-item, quantifiable assessment of overall neurologic function in infants.13 Section 2 of the HINE (HINE-2) assesses the development of motor function through the achievement of motor milestones; scores on the HINE-2 range from 0 to 26, with higher scores indicating better motor function.13,14 The HINE-2 involves evaluation in eight motor-milestone categories: voluntary grasp, kicking, head control, rolling, sitting, crawling, standing, and walking. For this primary end point, infants who had been enrolled for at least 6 months were evaluated in seven of the eight categories (excluding voluntary grasp) at screening, before the procedure on days 183 and 302, and on day 394. The infants were considered to have a motor-milestone response if they met the following two criteria: improvement in at least one category (i.e., an increase in the score for head control, rolling, sitting, crawling, standing, or walking of ≥1 point, an increase in the score for kicking of ≥2 points, or achievement of the maximal score for kicking) and more categories with improvement than categories with worsening (i.e., a decrease in the score for head control, rolling, sitting, crawling, standing, or walking of ≥1 point or a decrease in the score for kicking of ≥2 points). Infants who died or were withdrawn from the trial were considered to have had no response, regardless of whether they attended the visit on day 183.
The second primary efficacy end point was event-free survival, which was defined as the time to death or the use of permanent assisted ventilation (tracheostomy or ventilatory support for ≥16 hours per day for >21 continuous days in the absence of an acute reversible event). The use of permanent assisted ventilation as of days 91, 182, 273, 364, and 394 was determined on the basis of patient data from parental diaries and hospital records obtained at those visits. All events of permanent assisted ventilation were adjudicated by an independent end-point adjudication committee whose members were unaware of the group assignments.
Descriptions of the six secondary end points are provided in the Supplementary Appendix. Scores on the Children’s Hospital of Philadelphia Infant Test of Neuromuscular Disorders (CHOP INTEND) range from 0 to 64, with higher scores indicating better motor function; a CHOP INTEND response was defined as an increase of at least 4 points from baseline in the CHOP INTEND score at the end-of-trial visit (day 183, 302, or 394).15,16 A compound muscle action potential (CMAP) response was defined as an increase in the peroneal CMAP amplitude to at least 1 mV (or maintenance of an amplitude of ≥1 mV) at the end-of-trial visit (day 183, 302, or 394). Adverse events included all untoward events that occurred during the trial period, including those that were expected to occur in a population of infants with spinal muscular atrophy; details are provided in the Supplementary Appendix. Other safety assessments included vital-sign measurements, laboratory tests, and neurologic examinations.
In accordance with the statistical analysis plan, only the first primary efficacy end point was statistically assessed in the interim analysis. Because the P value for the first primary end point was significant in the interim analysis, this end point was not tested for significance in the final analysis. The second primary efficacy end point and all secondary efficacy end points were assessed in the final analysis. A hierarchical testing strategy was used to control the overall type I error rate at 0.05; in the final analysis, end points were ranked and tested for statistical significance in a hierarchical order (see the Supplementary Appendix).17
The difference between the nusinersen group and the control group in the proportion of infants who had a motor-milestone response was analyzed with the use of Fisher’s exact test. Event-free survival and overall survival were assessed with the use of a log-rank test that was stratified according to disease duration at screening (≤12 weeks or >12 weeks). The median time to death or the use of permanent assisted ventilation in each group and associated 95% confidence intervals were estimated with the use of the Kaplan–Meier product-limit method; probability of survival was estimated with the use of the Kaplan–Meier method. A hazard ratio for death or the use of permanent assisted ventilation and a hazard ratio for death were calculated with the use of a Cox proportional-hazards model that was adjusted for disease duration at screening in each infant. A hazard ratio of less than 1.00 indicated a lower risk of an event in the nusinersen group than in the control group. For details about patients included in the final analysis, see Figure S1 in the Supplementary Appendix.