Spinal Muscular Atrophy (SMA) is a rare genetic neuromuscular disorder that affects the central nervous system, peripheral nervous system, and voluntary muscle movement. It is characterized by the loss of motor neurons in the spinal cord, leading to progressive muscle weakness and atrophy (when muscles get smaller). SMA is typically diagnosed in infancy or early childhood, but it can also appear later in life with a milder course of the disease.
The most common form of SMA is caused by a mutated or missing gene known as the survival motor neuron gene 1 (SMN1), which is responsible for the production of a protein essential to motor neurons. There are four types of this form of SMA, classified based on the age of onset, symptoms, and rate of progression:
- Type 1: Also known as infantile-onset SMA or Werdnig-Hoffmann disease, this type affects infants from birth up to 6 months of age, with most babies showing signs of the disease by 3 months. It is the most severe form of SMA, and without treatment, it is the most common genetic cause of infant death.
- Type 2: This type usually appears in early childhood, and children with type 2 SMA can sit without support but may have difficulty walking and performing other motor tasks.
- Type 3: Also known as Kugelberg-Welander disease, type 3 SMA is seen after 18 months of age. Children can walk independently but may have difficulty doing so, running, rising from a chair, or climbing stairs. Other complications may include curvature of the spine, contractures, and respiratory infections. With treatment, most individuals can have an average lifespan.
- Type 4: This type of SMA typically appears in adulthood, and its symptoms can vary widely. People with type 4 SMA may experience mild to moderate muscle weakness and have a normal lifespan.
SMA can significantly affect quality of life and life expectancy, as it is a progressive disease that gets worse over time. Supportive care for SMA includes physical therapy, occupational therapy, respiratory support, nutritional support, orthopedic interventions, and mobility support. In recent years, there have been advancements in disease-modifying and gene replacement therapies for SMA, offering new hope for patients.
