Spinal Muscular Atrophy, or SMA, is a genetic neuromuscular condition where patients gradually lose muscle strength, affecting the patient’s ability to sit up, walk and, in severe cases, the ability to breath and swallow.
The disease is autosomal recessive and caused by genetic variants in the survival motor neuron 1 (SMN1) gene, leading to very low levels of the SMN protein which is crucial for functional motor neurons. In 95% of SMA patients the disease is caused by a homozygous deletion of exon 7 of SMN1.
There are four types of SMA, Type I – Type IV, with different levels of severity and age of onset. The severity is associated with the number of copies of the homologous SMN2 gene which can serve as a ‘backup’ gene. In its most severe form, Type I, also referred to as infantile onset SMA or Werdnig-Hoffmann disease, infants show symptoms within six months from birth, and the life expectancy without pharmaceutical treatment is less than 2 years.
SMA is a leading genetic cause of infant mortality, with prevalence estimates of 1 in 6,000 to 1 in 10,000 live births and a carrier frequency as high as 1 in 54. Until recently, SMA patients could receive symptomatic treatment but there was no effective treatment for the underlaying cause of the disease. However, since 2016, innovative pharmaceuticals and gene therapies enabling the patient to produce functional SMN protein has been approved. These new treatments have led to a high demand for including SMA on recommended newborn screening panels in several countries.
Newborn screening for SMA can detect the genetic variant in the SMN1 gene before symptoms appear and allow for the earliest possible treatment with the opportunity to delay muscular degeneration. Due to this fast-moving field, there are few long-term studies on early-onset treatment prognosis, but it is expected to offer a higher quality of life for patients for as long as possible.
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