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Mouse study offers hope for treating leading genetic cause of infant death

28 November 2011
Appeared in BioNews 635

Researchers have made a step forward in the treatment of spinal muscular atrophy, a serious genetic disorder, by using a stretch of RNA to trigger mice into producing a back-up version of a missing protein.

Spinal muscular atrophy, a genetic disease causing progressive muscular weakness, particularly affects children. People with the disease are missing a gene, SMN-1, which codes for the protein SMN. This protein supports and maintains motor neurones, and without it, messages are not passed from nerves to muscles. There is a 'back-up' version of the gene, known as SMN-2, but this produces lower levels of SMN, along with partly-functioning versions of the protein, and the severity of spinal muscular atrophy depends on the number of copies of the back-up gene.

The researchers used a mouse model of spinal muscular atrophy that had been engineered to carry a partly functioning version of the gene SMN-2. The mice were given a synthetic stretch of RNA that triggered the back-up gene to make full copies of the SMN protein, and these mice lived longer, moved better and gained more weight.

This is a study using a mouse model of the disease, so the treatment of humans, even in clinical studies, is still a way off. The next step for the team is to carry out tests on transgenic pigs with spinal muscular atrophy, which have been newly developed for this project. If these are successful, however, this could lead to a treatment for a currently incurable and often fatal disease, and could open up research in other similar inherited disorders.

Chris Lorson, researcher at the Bond Life Sciences Center, professor in the Department of Veterinary Pathobiology and the Department of Molecular Microbiology and Immunology and co-author of the study, said: 'It's been remarkable to watch how quickly SMN-2 knowledge has transformed from basic molecular biology to being modified targets for novel therapeutics. SMN-2 is like a light that's been dimmed, and we're trying anything to get it brighter. Even turning it up a little bit would help dramatically'.

Spinal muscular atrophy is the leading genetic cause of infant death worldwide, and the second leading cause of neuromuscular disease, affecting one in 6000 people. It not always fatal during childhood, however, and patients with less severe forms of the disease may survive into adulthood and occasionally old age. Around one in 30 people carry a copy of the defective gene causing spinal muscular atrophy, and if two carriers have a child, each child has a one in four chance of having spinal muscular atrophy.

Bifunctional RNAs Targeting the Intronic Splicing Silencer N1 Increase SMN Levels and Reduce Disease Severity in an Animal Model of Spinal Muscular Atrophy
Molecular Therapy |  25 October 2011
Synthetic RNA Lessens Severity of Fatal Disease
Science Daily |  21 November 2011
Synthetic RNAs and transgenic pigs advance the fight against SMA
Christopher S. Bond Life Sciences Centre |  18 November 2011
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