A drug used for spinal muscular atrophy (SMA)—a rare genetic disorder that causes muscle weakness and atrophy and respiratory problems—improved muscle control in children between the ages of 8 months and 9 years. These are the results of a study published online in Neurology in August.
In 2016, the US Food and Drug Administration (FDA) approved nusinersen, the first drug to treat all forms of SMA in children and adults. In SMA, nerve cells in the spinal cord are attacked, which leads to muscle weakness that can affect breathing, swallowing, walking, and head control. Nusinersen works by increasing the production of a specific protein vital for survival of motor neurons in the spinal cord.
SMA type 1, the most common and severe form of the disease, usually appears in infants at 6 months of age and has a median survival rate of eight to 14 months. Earlier studies on nusinersen for SMA1, which were conducted on infants younger than 7 months, found those treated with the drug were more likely to be alive and show improvements in motor function than those in placebo groups.
To observe the safety and efficacy of nusinersen in SMA1 patients older than 7 months, a team of researchers injected the drug into the spinal canals of 33 children. Participants were assessed prior to treatment as well as two months and six months after receiving treatment. Researchers collected data on survival, breathing, whether the children needed help eating, and their ability to move.
After receiving their first injection, five of the 33 children, ranging from 18 months to 4 years old, sat up without support for the first time.
At the six-month mark, all 33 participants were alive and continuing treatment. The researchers reported no safety concerns. On average, the group, including one 8-year-old, showed improvements in muscle control of 1.5 points, based on an infant motor milestone assessment.
A total of eight participants experienced worse respiratory status even in those who had improved motor function. The researchers suggested that respiratory symptoms and related infections that might destabilize weak patients may be slower to respond to nusinersen. None of the children needed more or less nutritional support such as a feeding tube.
While the researchers were focused on motor function, many of the parents of the participants reported other improvements such as a louder voice, better endurance, and more efficient coughing. "Better definition of these outcomes might be useful for long-term follow-up of these patients," the researchers concluded. Future studies should include a larger number of older patients to determine which SMA1 patients will be most responsive to treatment.
Overall, the researchers agreed nusinersen is beneficial for patients with SMA1 between 7 months and 9 years of age.