(Adds data from infant trial, updates share prices)
Feb 21 (Reuters) - Shares of Isis Pharmaceuticals reached a new high on Friday after the company said early trials of its experimental treatment for a rare spinal disorder showed that it increased muscle function in children and kept infants with the most severe form of the disease alive and off ventilators.
Isis is developing the "antisense" drug, known as ISIS-SMNRx, in partnership with Biogen Idec to treat spinal muscular atrophy. Isis is a leader in the field of antisense, which aims to interfere at the genetic level to regulate formation of disease-causing proteins.
Shares of Isis rose 16 percent to close at $59.00 on the Nasdaq exchange. Shares of Biogen gained 3.6 percent to close at $347.11.
Spinal muscular atrophy (SMA), which affects around 35,000 patients in the United States, Europe and Japan, is caused by a loss of, or defect in, a gene associated with the survival motor neuron protein.
Isis said children with SMA treated with the highest dose of the drug had an average 3.7-point increase in muscle function after nine months. In addition, a recently developed biomarker test showed increases in levels of a protein critical to health and survival of nerve cells in the spinal cord.
It also reported interim results from a trial of infants with type 1 SMA, showing that all four babies in the low-dose arm of the study were alive without needing respiratory assistance after being in the study for over six months. The four have an average age near 12.5 months.
Typically, about half of infants born with the most severe form of SMA will not make it to their first birthday and most will not make it to their second birthday, Dr. Tom Crawford, professor of neurology and pediatrics at Johns Hopkins Children's Center and a study investigator, said in a statement.
Isis said one infant in the high-dose arm of the trial died due to pneumonia early in the treatment portion of the study.
In the trial of older children, two patients experienced serious side effects, but they were not considered to be related to the drug.
"We do think these data support the bull case on the program, although there are still questions on magnitude and safety at higher doses," UBS Securities analyst Matthew Roden said in a research note. "However, with no effective treatment for SMA..., the bar is low."
He said ISIS-SMNRx is not included in his earnings estimates for Isis, but noted that bullish analysts have estimated sales at $1 billion a year.
Isis said it plans to start a pivotal-stage trial of the antisense drug in infants with spinal muscular atrophy in the middle of this year and a similar study in children later this year.
The company said it will present additional details from the earlier-stage SMA trials at upcoming medical conferences.
(Reporting By Deena Beasley; Editing by Jonathan Oatis and Leslie Adler)