People afflicted with Spinal muscular atrophy (SMA), received a special Christmas present from the FDA last week, which approved the use of a new drug Nusinersen (trade name Spinraza) to treat the muscle wasting disorder. SMA is caused by am an inherited genetic defect in the SMN1 gene, which encodes a protein necessary for “survival” of motor neurons. Without the proper levels of the SMN protein, the body loses function of neuronal cells in the anterior horn of the spinal cord, which in turn results in muscles atrophy, generally beginning with the lower extremities, followed by muscles of upper extremities, spine and neck and, in more severe cases, lungs.
It is considered one of the most common causes of genetic infant deaths, beginning during the initial months after birth with a rapid (and unexpected) onset of “floppy baby syndrome”. In fact, babies diagnosed with SMA type 1 do not generally live past 2-years of age, with death occurring as early as within weeks in the most severe cases. Other variations can also develop at any age, including adults.
The intermediate form generally begins between 6 and 18 months. These children may be able to sit at the onset but are never able to stand and walk, while the “ juvenile” form of spinal muscular atrophy usually manifests after 1-year of age. These toddlers are able to walk without support at some time, although many later lose this ability. In addition, respiratory involvement is less noticeable, and life expectancy is normal or near normal. The same is said for those who may develop it as adults over the age of 30.
Spinraza, which is injected directly into the fluid surrounding the spinal cord once every 4-months, can be used for patients of any age. According to Dr. Billy Dunn, M.D., director of the Division of Neurology Products in the FDA’s Center for Drug Evaluation and Research, its efficacy was determined in a clinical trial in 121 patients with infantile-onset SMA who were diagnosed before 6 months of age and who were less than 7 months old at the time of their first dose. In the end, results showed that nearly 40% of patients treated with Spinraza “achieved improvement in motor milestones (as defined by researchers), whereas none of the control patients did.
Meanwhile, the most common side effects from the drug were found to be upper and lower respiratory infections as well as constipation. Additional warnings, however, were issued in regard to low blood platelet count and toxicity to the kidneys.