Spinal muscular atrophy: what is this disease that must be detected as soon as possible?

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Spinal muscular atrophy: what is this disease that must be detected as soon as possible?

It took a total of 917,000 SMS, or a twelfth of the Belgian population, to collect 1.9 million euros, good news for the parents of Pia, a nine-month-old Belgian baby, suffering from spinal muscular atrophy. While screening for the disease has been automatic in Wallonia since March 2018, little Pia had the misfortune to be born in Flanders, where screening is not available. Her spinal muscular atrophy has been detected too late and, for the time being, her life expectancy does not exceed two years, if she does not follow a treatment, available only in the United States. The money raised by the fundraising is thus intended to finance the treatment that would allow it to better cope with this rare hereditary disease.

What is spinal muscular atrophy?

This rare disease of genetic origin can be fatal in some cases, such as that of a young child. Indeed, it is characterized by weakness and muscle atrophy, at birth, during childhood or in adulthood, due to DNA abnormalities. In particular, it can prevent the lungs and heart from functioning, hence the interest of detecting it, in the first months of a baby's life. As revealed by the Telethon association, abnormalities damage the nerve cells, called the motor neurons, located in the spinal cord, which control the muscles. This degradation thus leads to the injury and death of the motor nerves through which the movement control passes. The order of movement is thus no longer transmitted to the muscles, thus rendering them inactive, weakened and atrophied.

Depending on the affected muscles, the affected nerve cells are classified as proximal spinal muscular atrophy. Infant spinal muscular atrophy (ASI) is linked to the SMN1 gene. Its absence or defectiveness is thus not able to give the right information to produce a protein called SMN ("motor neuron survival protein").

The doctors distinguish 4 different types of proximal spinal muscular atrophy, according to the age of onset of the first symptoms:

• type I spinal muscular atrophy (or spinal muscular atrophy type I or Werdnig-Hoffmann disease),

• type II spinal muscular atrophy (or spinal muscular atrophy type II),

• Type III spinal muscular atrophy (or Kugelberg-Welander disease),

spinal muscular amyotrophy type IV.

What are the symptoms of spinal muscular atrophy?

• Muscular weakness, of varying severity, damaging motor and respiratory capacities

• A loss of reflex

• Tremor of hands and fingers

• Deviation and twisting of the spine (scoliosis), muscle contractions and joint contractions in children

• Significant constipation

• Gastroesophageal reflux (heartburn and acid regurgitation)

• Difficulty walking, running, climbing stairs and getting up

Spinal muscular atrophy: what treatments?

There are currently only two types of expensive treatments for treating spinal muscular atrophy. Developed by the laboratories Ionis Pharmaceuticals and Biogen, the nusinersen, also called Spinraza, can be prescribed in France, since obtaining the European marketing authorization in June 2017. This drug is administered by an inthratecal injection (in the lower spine) during specialized consultations "Neuromuscular diseases" and is reimbursed for people suffering from proximal spinal muscular atrophy type I, II and III. The Spinraza, worth 500,000 euros the first year and 250,000 euros the following years, does not allow healing, but slows the symptoms of the disease. The second treatment available is Zolgensma gene therapy, developed by the AveXis laboratory and now by the Novartis laboratory. This therapy amounts to 1.9 million euros for the single injection. Its cost is justified by a major biological advance that consists of replacing the defective SMN1 gene with a therapeutic SMN1 gene. However, this treatment is currently marketed only in the United States. An application for a marketing authorization from the European health authorities is currently being examined.

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