Spinal Muscular Atrophy

Cause of the disease

The cause of SMA is a mutation in the SMN1 gene, which normally provides the blueprint for a vital protein: the SMN protein (Survival of Motor Neuron). This protein is needed throughout the body, but especially in motor neurons.

Many people also have the SMN2 gene, which can produce a certain amount of functional SMN protein. The more copies of the SMN2 gene a person has, the milder the disease tends to be – although this correlation is not always reliable.

How common is SMA?

• Worldwide, 1 in 6,000 to 10,000 newborns is affected.

• Around 10 children are born with SMA in Switzerland each year.

• Approximately 1 in 40 people is a carrier of the defective gene (usually without knowing it).

• It is estimated that around 180 people in Switzerland live with SMA.

• Since 2024, every newborn in Switzerland is tested through newborn screening, allowing treatment to begin as early as possible, even before the first symptoms appear.

How does SMA develop?

The progression of spinal muscular atrophy (SMA) is highly variable: it ranges from the most severe forms in infants, with almost no motor development, to milder forms in adults who remain mobile despite muscle weakness.

The consequences of the disease may include loss of motor functions (e.g., the ability to walk), skeletal or spinal deformities, swallowing difficulties, feeding problems, digestive, respiratory and speech impairments, and increased fatigue.

Traditionally, the disease is classified into four types, from Type 0 (the most severe form) to Type 4 (the mildest form). This classification is based on the age at which symptoms first appear and the highest level of motor development achieved.

However, since the course of the disease can vary greatly and many patients do not fit precisely into one defined type,patients are described based on their current abilities and treatment is adjusted accordingly. Today, the main distinction is whether a person cannot sit, can sit, or can walk.