Type 1 SMA is a progressive neuromuscular disease that weakens the body's muscles and is the leading cause of genetic infant mortality. It is caused by a mutation in the gene that builds vital survival-of-motor-neuron (SMN) protein. It affects about 1 in 4,000 to 6,000 children. The age of onset occurs before 6 months and most infants never reach their second birthday.
Of the 41 infants treated, 29% met the 5-second-sit milestone after 12 months of therapy.
Chief author Dr. Basil Darras of Boston Children's Hospital told Reuters Health in a telephone interview that 24-month data, which is not part of the study released in The New England Journal of Medicine, shows that the children continue to improve, with 61% able to sit upright for 5 seconds.
"Someone can say five seconds isn't very long," he said. So the children have also been tested for 30 seconds. While 17% of the group could sit upright for at least 30 seconds at the 12-month mark, after 24 months of treatment, the rate was 44%.
The 24-month data were released at this year's meeting of the American Academy of Neurology.
The Darras team also regarded the treatment a success at 12 months if the child could score 40 or higher on a 65-point neuromuscular disorders scale; 56% met that benchmark compared to a rate of 17% based on historical controls.
The rates of survival without permanent ventilation were 85% and 42% respectively.
The drug is sold under the brand name Evrysdi by Roche, which paid for the study and helped run it. Of the three approved treatments for the condition, risdiplam is the only therapy given orally.
The drug increased the concentration of SMN protein in the blood, going from a median of 2.91 ng per milliliter at baseline, peaking to 6.75 at 17 weeks and dropping a bit to 5.17 at the 12-month mark.
In addition, "95% of the infants at 24 months were not only alive, but able to swallow normally, which is important because many lose their ability to swallow," Dr. Darras said.
The treatment is expensive, costing $100,000 to $400,000 per year depending on the size of the child.
However, the researcher said, "34% of the infants did not require hospitalization during that 24 months, which is an important finding. because admission to a hospital can cost you a lot of money."
There were 48 serious adverse events including pneumonia, hypotonia, bronchiolitis and respiratory failure. Three children had an adverse event with a fatal outcome, all due to SMA-related respiratory complications.
"Outside of some adverse events related to their disease, we didn't have any adverse events specifically related to risdiplam," said Dr. Darras, director of the Neuromuscular Center and SMA Program at Boston Children's.
The children continue to be treated with the drug as part of the initial 24-month open-label study and a 36-month extension.
SOURCE: https://bit.ly/2V8rdXw The New England Journal of Medicine, online July 28, 2021.
By Gene Emery
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