Spinal muscular atrophy (SMA) is an extremely rare genetic disorder that affects between one in 6,000 to one in 10,000 people. It is the cause of premature death in many young patients. However, scientists have developed a new experimental drug that has produced dramatic results, even making it possible for some children with SMA to walk again.
The drug is nusinersen, and the results of the recent trial were so overwhelmingly positive that the study was discontinued in August. It was decided it was unethical to keep a control group of children on a placebo when nusinersen was so effective in the treatment group.
Children who had been unable for years to even crawl responded to the medication by gaining strength and moving. Some even walked, with help.
The severity of the disease varies among patients, but in all cases it affects nerve cells and weakens muscles. After a year or two with SMA, many children are not longer able to sit on their own, to move their limbs, or even to swallow without assistance.
Researcher Francesco Muntoni from University College London described his feelings during the study:
To see children who would have been dead sitting and standing is something I never thought I would see.
The research team was one of several working around the world on “antisense treatments” like nusinersen. These are drugs that can interrupt expression of a particular gene. These therapies work by specially engineering a section of DNA to target certain RNAs (protein recipes) to alter the proteins they produce.
The main challenge to scientists is getting these DNA fragments to survive inside the body and penetrate the cells. Nusinersen seems extremely promising in this effort.
It has not yet been proven that nusinersen is the answer to spinal muscular atrophy, and the reports on the recent studies have not yet been published. But studies with mice indicate when the drug is injected, it is able to spread throughout the spinal cord and the brain.
The clinical trials of nusinersen are promising even beyond its affect on SMA. Scientists hope engineered antisense drugs can stop the expression of other specfic genetic defects such as Huntington’s disease, motor neurone disease, and Alzheimer’s disease.
