Nusinersen Beneficial in Spinal Muscular Atrophy Patients, Even When Started Late

In a new study, investigators in France and Belgium have found that a drug given to babies with spinal muscular atrophy before 7 months of age may still be beneficial when treatment is initiated in children ages 8 months and older.

The genetic disorder spinal muscular atrophy (SMA) is caused by specialized nerve cells in the spinal cord and brain stem. Without these necessary motor neurons, infants born with the type 1 (SMA1) form of this condition or those who develop symptoms in the first few months of life have developmental delays preventing them from sitting up unassisted, along with problems breathing and swallowing. Type 2 SMA (SMA2) typically develop muscle weakness between 6 and 12 months of age and can sit up unsupported but cannot stand or walk on their own. SMA types 3 and 4 have milder symptoms that develop later in childhood, adolescence, or adulthood.

Among infants born with SMA1, also known as Werdnig-Hoffmann disease, the majority do not live beyond 2 years of age due to respiratory failure. In December 2016, the FDA approved the drug nusinersen for the treatment of SMA1, which works by boosting production of protein motor neurons in the spinal cord needed to survive. While the drug has not been effective in all cases, with treatment, some infants have been able to reach developmental milestones such as sitting, crawling, and walking. While past studies have examined initiation of nusinersen treatment before the age of 7 months, a new study published online on August 29, 2018, in the journal Neurology indicates that patients who start treatment with the drug after 7 months of age can still see benefits.

For the study, conducted from December 2016 to May 2017, investigators treated 33 patients ranging in age from 8.3 months to 113.1 months with intrathecal injections of nusinersen to evaluate the safety and efficacy of the drug. The research team conducted evaluations before treatment was administered and then at 2 months and 6 months following treatment initiation. Using the modified Hammersmith Infant Neurologic Examination to assess motor function, the investigators observed that while response varied among patients, on average, there was a significant improvement in muscle control, even with the oldest study participant who was 8 years of age. The need for respiratory support also decreased during the course of the study period. In addition, 5 study participants between the ages of 18 months and 4 years old at the beginning of the study were able to sit up without support for the first time. At 6 months, all patients were alive and continuing treatment.

"This study is exciting because we found participants had motor function improvement 6 months after receiving treatment, even an 8-year-old participant," said study author Laurent Servais, MD, PhD, of Pitié-Salpêtrière Hospital in Paris, France and Citadelle Hospital in Liège, Belgium, in a recent statement. "The overall response was to the same extent as that in the previously studied younger population."

The authors note the limitation that the majority of patients enrolled in the study were under the age of 4.5 years but say that their findings indicate that even patients with more advanced SMA1 can benefit from nusinersen treatment.