Spinal muscular atrophy, a time-dependent pathology

Neonatal screening, commonly known as the heel prick test, is essential for detecting genetic diseases. Early diagnosis is crucial for saving lives or ensuring optimal development conditions, in the case of diseases such as spinal muscular atrophy (SMA). The Ministry of Health has recently announced the approval of a new nationwide neonatal screening that will reverse the inequality in access to this test between autonomous communities that existed until now.

SMA is a neuromuscular disease that manifests itself through a progressive loss of strength and can affect essential activities such as speaking, breathing, walking or swallowing. In Spain, between 800 and 1,000 people suffer from SMA, according to the Spanish Society of Neurology. “The development of treatments in the last decade has radically changed the survival and quality of life of SMA patients, but to do so we need to act before the first symptoms appear,” explains Juan Vázquez, a neurologist at the Neuromuscular Diseases Unit at the La Fe University and Polytechnic Hospital (Valencia).

When there was no treatment, these types of patients usually died within a few months or years. Today, with advances in drugs, they can have a better survival rate.

Juan Vázquez, neurologist at the Neuromuscular Diseases Unit at the La Fe University and Polytechnic Hospital (Valencia).

Different effects and prognoses

This disease is caused by the absence or mutation of the SMN1 gene, which is responsible for producing the SMN protein, which is essential for the survival of motor neurons and muscle development. For the disease to manifest and for symptoms to appear, the genetic alteration must be inherited from both parents. However, the body has another gene, SMN2, which can also produce SMN protein, although less efficiently. The number of copies of the SMN2 gene, which varies between individuals, significantly influences the severity of the disease and its prognosis.

SMA type I is the most severe. Symptoms appear during the first six months of life. “These are children who move less than normal, have decreased muscle tone, suck less when breastfeeding, have a weak cry or even respiratory failure, breathing with great agitation,” describes the neurologist. This is the most frequent manifestation: between 50% and 60% of cases. “When there was no treatment, these types of patients normally died in a few months or years. Today, with the advances in drugs, they can have a better survival rate,” he assures.

For type II and type III, symptoms appear later and, as the neurologist at the La Fe University and Polytechnic Hospital explains, “their progression is the loss of walking, and these are patients who survive into adulthood.”

Treatments that make a difference

In the case of adult SMA patients, treatment is essential to prevent the disease from progressing and further loss of autonomy. Since 2016, three drugs have been approved that have proven effective against the disease. In cases where it is applied before the first symptoms appear, it can even prevent motor sequelae, as Vázquez explains.

In Spain, routine genetic diagnosis came into effect in the late 1990s or early 2000s: so patients who were born earlier may have lived without having a genetic diagnosis and being told exactly what type of SMA they have.

The treatments – authorised only for individual use – have shown that in many cases they can stop the progression of the disease. “Even recovering part of what they had lost in the last two or three years. A very important advance for them, because the outlook they had was one of limited life expectancy and major disabilities,” Vázquez celebrates, adding the importance of having a genetic diagnosis that determines the specific type of SMA they suffer from.

“In Spain, routine genetic diagnosis came about in the late 1990s or early 2000s, so patients who were born earlier may have lived without having a genetic diagnosis and being told exactly what type of SMA they had,” says Vázquez. “20% or 30% of patients managed to reach adulthood, and then they lost follow-up. During their childhood years, they received proper follow-up, which was lost when they reached adulthood because they were told that nothing more could be done for them. Currently, there are patients living with SMA without knowing that they have it, or diagnosed but who do not know that new treatments have appeared,” he warns.