A population-based study conducted in the state of New York demonstrates the feasibility and benefits of newborn screening for spinal muscular atrophy (SMA). Supported by these findings, researchers recommend adding SMA genetic tests to the national recommended uniform screening panel. The study, “Pilot study of population-based newborn…
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A key player in a pathway known as the cell’s “cleaning system” could be a promising target for alternative approaches to treating spinal muscular atrophy (SMA), a mouse study suggests. The study, “Blocking p62-dependent SMN degradation ameliorates spinal muscular atrophy disease phenotypes,”…
Researchers in a mouse model of spinal muscular atrophy have discovered why certain nerve cells, called ocular motor neurons, are able to resist the damage and degeneration linked to the disease. SMA is caused by mutations in the SMN1 gene, considerably lowering the amount of the SMN protein produced. SMN, present in all cells, is necessary for the survival of motor nerve cells, or motor neurons, which are progressively lost during disease progression. In SMA, spinal motor neurons — nerve cells in the spinal cord that control skeletal muscle movements, including the arms and legs — are those mainly affected. Their loss leads to weakness and atrophy of skeletal muscles, affecting voluntary movement. For unknown reasons, certain types of cranial motor neurons in the brainstem — the region at the base of the brain that connects with the spinal cord — show partial or even no damage in SMA patients. Among cranial motor neurons, those that control the muscles of the tongue are affected to some extent, and those controlling the eyes — called ocular motor neurons — are resistant to SMA-associated degeneration. Understanding why ocular motor neurons are spared in SMA may help in developing new treatment approaches, particularly gene therapies, and in preventing progressive motor neuron loss. Using a mouse model of SMA, researchers conducted a comprehensive analysis of vulnerable and resistant nerve cell groups at several stages of the disease. They used an approach called LCM-seq that couples laser microdissection of cells from frozen tissues with analysis of gene expression. Dissected nerve cells came from the spinal cord and brainstem regions of healthy mice and mice at different stages of SMA: a pre-symptomatic stage, an early symptomatic stage (damage restricted to some regions of the spinal cord), and a symptomatic stage (clear motor dysfunction and extensive loss of spinal motor nerve cells). Researchers found 251 genes highly associated with SMA, from which 113 genes (45%) were differentially expressed to a significant degree in both disease-vulnerable and -resistant types of motor neurons from the SMA mice. In response to low SMN protein levels, all motor nerve cells showed significant expression of genes associated with stress-responses and cell death, independent of their vulnerability to SMA. To understand how — despite activated cell death signals — ocular motor neurons were able to resist damage due to SMA, the researchers compared the expression patterns of these resistant ocular motor neurons with those of vulnerable spinal motor neurons. They found signs of nerve cell dysfunction upon loss of SMN in the vulnerable neurons. But the resistant neurons rapidly and selectively adapted: they increased the expression of genes that are associated with cell survival, with protection from oxidative stress and cell death, and with regeneration and/or maintenance of communication signals between nerve cells and muscle cells. “We show that ocular motor neurons present unique disease-adaptation mechanisms that could explain their resilience,” the researchers wrote. They also noted these cell-specific mechanisms “present compelling targets for future gene therapy studies aimed towards preserving vulnerable motor neurons,” in the context of motor nerve cell diseases.
Walking ability in type 3 SMA patients is significantly impaired during adolescence, according to recent research. Type 3 SMA, also known as Kugelberg-Welander disease, is a milder form of SMA. Muscle weakness in type 3 SMA mainly affects patients’ limb movements, and children are generally able to stand and walk. These abilities decrease over time, however. Symptoms usually appear between 18 months and early teens. Symptom onset before age 3 is classified as type 3A SMA, and onset at later ages as type 3B — considered a milder SMA subtype. However, while SMA is thought to be a largely stable disorder, recent studies have highlighted different rates of progression based on age and function. In patients who cannot walk, gross motor function improves until about age 5, then worsens until about age 15, followed by a relatively stable phase in late adolescence and adulthood. While ambulatory patients have a similar disease progression to that of non-ambulatory patients, a more specific assessment may be necessary to identify changes in walking function. Researchers used data from three prospective natural history studies to evaluate changes in walking ability in 73 individuals with type 3 SMA who were able to walk without support for at least 10 meters. The team used the the six-minute walk test, a valid and reliable functional assessment that measures the distance a person can walk in six minutes. While the 6MWT was initially developed to evaluate functional exercise capacity in heart- and lung-associated diseases, it has become a valuable and reliable test to measure functional walking ability in SMA patients. The study showed that the ability to walk strongly deteriorated during adolescence with a loss of 20.8 meters per year, and slowly declined again through adulthood with a loss of 9.7 meters per year. The age around puberty appeared to be the most vulnerable period in ambulant patients, with researchers hypothesizing that weight gain and growth associated with puberty could contribute toward a greater decline in walking capacity. The study authors emphasized that when designing future clinical trials with SMA patients, it is important to understand the natural history of the disease and identify disease trajectories as measured by the 6MWT to better interpret patients' response to treatment.
Taking care of a child with spinal muscular atrophy (SMA) significantly affects several aspects of families’ lives, including finances, career choices, social life, and mental health, according to an Australian study. The study, “Financial, opportunity and psychosocial costs of spinal muscular atrophy: an exploratory qualitative analysis…
Reldesemtiv improved muscle strength for walking and respiration in a dose-dependent manner in spinal muscular atrophy (SMA) patients, data from a Phase 2 clinical trial show. As a fast muscle activator, reldesemtiv will not treat the underlying causes of SMA — a lack of the SMN protein to nourish muscles…
A new way of restoring potentially adequate levels of survival motor neuron (SMN) — the protein missing in spinal muscular atrophy (SMA) — uses small molecules that target the structure of an intermediate player in this protein’s production. The study on this approach, “Targeting RNA structure in SMN2…
A pathway known as the cell’s “cleaning system” may be a promising target of alternative approaches to treating spinal muscular atrophy (SMA) — ones that look beyond the disease-causing mutation. This possibility is the focus of the perspective article, “Autophagy inhibition: a…
Two specific mutations may help in identifying people who are carriers of spinal muscular atrophy (SMA) — those who do not have the disease but can pass it to children — and should be aware before starting a family, a study from Spain reports. The study, “Utility…
Neurological health depends as much on signals sent by the body’s leg muscles to the brain as it does on those sent from the brain to the muscles, according to a recent study. These results offer new clues as to why patients with neurological diseases such as spinal muscular atrophy (SMA)…
