MU researchers find synthetic RNA lessens severity of fatal disease
A team of University of Missouri researchers have found that targeting a synthetic molecule to a specific gene could help the severity of the disease Spinal Muscular Atrophy (SMA) – the leading genetic cause of infantile death in the world.
“When we introduced synthetic RNA into mice that carry the genes responsible for SMA, the disease’s severity was significantly lowered,” said Chris Lorson, researcher at the Bond Life Sciences Center and professor in the Department of Veterinary Pathobiology and the Department of Molecular Microbiology and Immunology. “The mice that receive synthetic RNA gain more weight, live longer, and had improvements in motor skills. These results are very exciting.”
SMA is a rare genetic disease that is inherited by one in 6,000 children, who often die young because there is no cure. Children who inherit SMA are missing a gene that produces a protein which directs nerves in the spine to give commands to muscles. Lorson’s lab focuses on targeting a partially functioning back-up copy of the missing gene, known as SMN-2, into producing the needed protein.
While the results are promising, Lorson notes additional research is needed before synthetic RNA could be used on humans for SMA. Clinical trials for similar synthetic RNAs are currently being performed in other neurodegenerative disease such as Lou Gehrig’s or ALS. In SMA, there are clinical trials taking place in many labs across the country that are investigating drug compounds to increase SMN-2 protein production.
Spinal muscular atrophy (SMA) is a genetic disease that attacks nerve cells, called motor neurons, in your spinal cord. These neurons communicate with your voluntary muscles - the ones you can control, like in your arms and legs. As you lose the neurons, your muscles weaken. This can affect walking, crawling, breathing, swallowing and head and neck control.
SMA runs in families. Parents usually have no symptoms, but still carry the gene. Genetic counseling is important if the disease runs in your family.
There are many types of SMA, and some of them are fatal. Life expectancy depends on the type you have and how it affects your breathing. There is no cure. Medicines and physical therapy help treat symptoms.
NIH: National Institute of Neurological Disorders and Stroke
“It’s been remarkable to watch how quickly SMN-2 knowledge has transformed from basic molecular biology to being modified targets for novel therapeutics,” Lorson said. “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.”
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The study, “Bifunctional RNAs Targeting the Intronic Splicing Silencer N1 Increase SMN Levels and Reduce Disease Severity in an Animal Model of Spinal Muscular Atrophy,” was published in the journal Molecular Therapy. Co-authors include Erkan Osman and Pei-Fen Yen of the University of Missouri.
The central role of lower motor neuron degeneration was confirmed in subsequent pathologic studies demonstrating a loss of anterior horn cells in the spinal cord and cranial nerve nuclei.
Since then, several types of spinal muscular atrophies have been described based on age when accompanying clinical features appear. The most common types are acute infantile (SMA type I, or Werdnig-Hoffman disease), chronic infantile (SMA type II), chronic juvenile (SMA type III or Kugelberg-Welander disease), and adult onset (SMA type IV) forms.
The genetic defects associated with SMA types I-III are localized on chromosome 5q11.2-13.3.
Many classification systems have been proposed and include variants based on inheritance, clinical, and genetic criteria. Among these are the Emery , Pearn , and International SMA Consortium system . The ISMAC system is most widely accepted and is used in this review.
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Spinal Muscular Atrophy kills more babies than any other genetic disease.
Degeneration and death of the motor neurons (also called Anterior Horn Cells) in the brain stem and spinal cord produces weakness in the muscles of swallowing, breathing, and limbs. This disease afflicts infants, children, and adults worldwide. It is estimated that spinal muscular atrophy occurs in between one-in-6,000 and one-in-20,000 births. Advances in our understanding of the genetics of this disorder confirm that the majority of children and adults afflicted with SMA, have inherited this disorder by receiving one gene from both their mother and their father. This is termed “autosomal recessive genetic transmission.”
Between one-in-40 and one-in-80 “normal” men and women carry the gene for spinal muscular atrophy. If both a man and woman carry the gene, the chances are 25% that any of their children will manifest SMA.
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Steven Adams
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University of Missouri-Columbia