On December 23rd, the FDA approved a drug to treat spinal muscular atrophy, the most common cause of childhood death. SMA affects the motor neurons in the spinal cord and brain stem responsible for movement, which includes swallowing and breathing. The most destructive form of SMA proves fatal around the age of 2, most often as a result of suffocation. Until the 23rd, no drugs had been approved by the FDA for the treatment of SMA. Trials in November showed that the new drug, called nusinersen, successfully allowed cells to bypass the genetic flaw that leads to SMA.
Jeffrey Rothstein, a neurologist at the Johns Hopkins School of Medicine in Baltimore, said:
“These [infant-onset] SMA kids are going to die. And not only are they now not dying, you are essentially on the path to a true cure of a degenerative [neurological] disease, which is unheard of.”
Rothstein was not involved in the drug trials or the two companies involved in creation of the drug.
Roughly 1 in 10,000 infants are estimated to suffer from SMA, carried by about 1 in 50 adults who are unaffected by the disease. Two adult carriers have a 25 percent chance of yielding offspring affected by SMA. Milder forms of SMA can allow children to survive longer, even living into adulthood. Children with SMA are missing, or have a defective version of, the protein produced by the SMN-1 gene. The role of the protein is still not well understood by scientists, but without it, motor neurons die off.
Some children carry varying amounts of copies of the SMN-2 gene, which produces a smaller amount of the protein. With enough copies of SMN-2, these children can survive considerably longer.
The foundation was laid for nusinersen in 2003 at Cold Sping Harbor Laboratory in New York , where Adrian Krainer and a colleague created a synthetic, RNA-like molecule. The molecule is able to alter the way the SMN-2 gene gets transcribed into the messenger RNAs that are translated to produce the relevant protein. Neuroscientist Frank Bennett took notice of the work, and contacted Krainer. The resulting collaboration led to the development of the drug – basically a piece of RNA called an antisense oligonucleotide, which ensures that the SMN-2 gene produces the full SMN protein during the transcription process. Drug trials began in 2011, and scientists reported success extending life spans and enhancing the motor function of children affect by SMA.