What is SMA?

What is SMA?
Spinal muscular atrophy is a genetically inherited neuromuscular disease characterized by progressive muscle weakness and atrophy. Research studies have discovered that SMA is caused by a mutation of the survival of motor neuron (SMN) gene. The SMA gene is presented in two nearly identical copies (SMN1 and SMN2) in the human genome. The absence of a functional SMN1 gene results in a significant decrease in the production of SMN protein which is crucial for the survival of spinal cord motor neurons. Without this protein, the motor neurons in the spinal cord degenerate and die.

How common is SMA?
SMA occurs in about 1 in every 6,000-10,000 births, regrettably qualifying it as the number one genetic killer of babies and toddlers under the age of two.

SMA is an autosomal recessive motor neuron disease, meaning that both parents have to be carriers. It is currently estimated that 1 in 35 people are carriers for SMA-that's about 7.5 million Americans.

How does SMA affect children?
Spinal Muscular Atrophy rapidly destroys a child's muscle control and strength, leading to the progressive inability to walk, stand, sit up, swallow, and ultimately, breathe.

In 80% of the most common and severe cases (Type I), the weakness is so great that death occurs before the age of one. Those that survive suffer from severe muscle atrophy, limiting all but the most miniscule of muscle movements.

Children with SMA are at risk for fatal respiratory complications. Life supporting equipment is often used to help clear a child's airway and lungs to prevent choking and pneumonia. Most children endure repeated surgeries, which may include procedures to help with feeding, spinal deformities and contractures.

What are the different types of SMA?
There are three types of childhood SMA as well as an adult form. Each is listed below with a general description of symptoms and the average age when children exhibit weakness.

Type I
Type I is the most common and severe form of SMA. 60% of children diagnosed with SMA are in this category. Diagnosis is usually made by six months of age, and babies will never develop the ability to sit, stand or walk. Some common symptoms of this type are a weak cry, trouble swallowing as well as sucking, and breathing distress. Type I children will never reach milestones like rolling, lifting their head or sitting up.

Type II
Type II babies will not normally exhibit symptoms at birth. The prognosis for life expectancy, or for independent standing or walking, roughly correlates with how old they are when they first begin to experience symptoms. Older children tend to have less severe symptoms, with onset between 6 and 12 months. Type II children will loose or never develop the ability to sit up.

Type III
Children diagnosed with type III have difficulty with normal motor functions such as walking. Onset is after 12 months of age, and children with onset after 18 months are often able to walk and remain fully functional for years before they need assistance. It is possible for a child with type III to reach a normal life expectancy.

Type IV
Type IV is typically referred to as adult onset. Adult onset SMA will typically occur after 35 years of age.