according to an analysis presented at the 2020 CNS-ICNA Conjoint Meeting, held virtually this year.
“Children are developing in a manner more consistent with normal development than that expected for children with two and three SMN2 gene copies,” said Russell Chin, MD, a neurologist at New York–Presbyterian Hospital. “These data demonstrate the durability of effect over a median of 3.8 years of follow-up, with children aged 2.8-4.8 years at the last visit.”
Many participants in the study achieved motor milestones within normal time limits, and no participant lost any major motor milestones. The investigators did not identify any new safety concerns during a maximum of 4.7 years of follow-up. They will follow participants until they reach approximately 8 years of age.
An ongoing open-label study
Dr. Chin presented interim results of the ongoing NURTURE study, which is examining the efficacy and safety of intrathecal nusinersen when administered to presymptomatic infants with SMA. The open-label, single-arm, phase 2 study is being conducted in various countries. Eligible participants were 6 weeks old or younger at first dose and had two or three copies of SMN2. The primary end point of NURTURE is time to death or respiratory intervention (i.e., invasive or noninvasive ventilation for 6 or more hours per day continuously for 7 or more days or tracheostomy). The natural history of SMA type 1 indicates that the median age at death or requirement for ventilation support is 13.5 months.
The investigators enrolled 25 infants: 15 with two copies of the gene and 10 with three copies. At the February 2020 interim analysis, participants had been in the study for 3.8 years and were aged 2.8-4.8 years at the last visit. No children had discontinued treatment or withdrawn from the study. All participants are alive, and four participants (all of whom have two copies of SMN2) required respiratory intervention. The latter children initiated respiratory support during an acute reversible illness. No subjects have required permanent ventilation, which the investigators define as ventilation for 16 or more hours per day for more than 21 days in the absence of an acute reversible event, or tracheostomy.
Treatment improved motor development
Approximately 84% of children achieved a maximum score on the Children’s Hospital of Philadelphia Infant Test of Neuromuscular Disorders (CHOP INTEND) scale. The population’s mean CHOP INTEND score increased steadily from baseline and stabilized at approximately the maximum score of 64. The population’s mean change in CHOP INTEND score from baseline to last visit was 13.6 points. The mean score at last visit was 62.0 among patients with two copies of SMN2 and 63.4 among patients with three copies. In addition, the time to first achievement of maximum CHOP INTEND score was shorter in participants with three copies of SMN2, compared with those with two. Four participants with two copies of the gene have not yet achieved a maximum CHOP INTEND score.
Many of the children in the study achieved World Health Organization motor milestones within time frames consistent with normal development. About 84% of participants became able to sit without support within the normal time frame in healthy children. Approximately 60% of children achieved walking with assistance within the normal window, and 64% achieved walking alone within the normal window. Of 25 participants, 24 are walking with assistance, and 22 of 25 (88%) can walk alone. Dr. Chin and colleagues observed that lower levels of phosphorylated neurofilament heavy chain in plasma and cerebrospinal fluid on treatment at day 64 were significantly correlated with higher total score on the Hammersmith Infant Neurological Examination at day 302 and with earlier achievement of the WHO milestone walking alone.
Nusinersen and lumbar puncture were well tolerated. No children discontinued treatment or withdrew from the study because of an adverse event. The investigators did not consider any adverse events or serious adverse events to be related to the study drug. They also did not observe any clinically relevant trends related to nusinersen in hematology, blood chemistry, urinalysis, coagulation, vital signs, or ECGs.
Dr. Chin is an employee of and holds stock in Biogen, which manufactures nusinersen and is sponsoring the study.
SOURCE: Chin R et al. CNS-ICNA 2020, Abstract PL78.