Before a couple decides to have a baby, they have the option of getting a special preconception (before conception) test, called carrier testing, that helps them understand if they are at risk of passing on certain genetic conditions to their children. One such condition is spinal muscular atrophy, a disorder characterized by muscle weakness and decay. This condition affects an individual’s ability to walk, eat, and sometimes even breathe. It is the second most common cause of neuromuscular disease and the most common genetic cause of infant deaths. 

How is Spinal Muscular Atrophy Inherited?

Spinal muscular atrophy (SMA) is an inherited genetic disorder. Inherited genetic disorders only develop when an individual inherits a gene from his/her parents with a specific mutation associated with the disease. There are many different types of inherited genetic disorders. Spinal muscular atrophy is a recessive disorder. This means that each parent must pass on a mutated gene associated with SMA in order for their child to develop the condition — if the child only inherits one copy of the mutated gene, he/she will not develop the condition. 

How Does Spinal Muscular Atrophy Develop?

The defining symptoms of SMA, weakness and loss of skeletal muscle mass, develop when motor neurons, cells that control muscle movement, begin to disappear.

What is the Life Expectancy of an Individuals Diagnosed With Spinal Muscular Atrophy?

The expected lifespan for individuals diagnosed with spinal muscular atrophy varies from person to person. The main indicator as to how long an individual diagnosed with spinal muscular atrophy may live is the type of spinal muscular atrophy they develop. There are five types of spinal muscular atrophy — each type is caused by a different mutation on the same gene:

  • Type 0 — The most severe and rarest type of SMA. Babies with SMA oftentimes don’t live past infancy.
  • Type I — Also referred to as Werdnig-Hoffmann disease, the most common type of SMA. Most children born with SMA do not live past childhood. 
  • Type II — Also referred to as Dubowitz disease, develops in babies between the age of six and 12 months. Children who develop Dubowitz disease can live into their twenties or thirties, although this will vary for each individual. 
  • Type III — Also referred to as Kugelberg-Welander disease, develops in children after early childhood. Children who develop Kugelberg-Welander disease tend to have a normal life expectancy and may require a wheelchair later in life. 
  • Type IV — Develops in early adulthood and causes mild to moderate muscle weakness. Individuals who develop Type IV SMA tend to have a normal life expectancy. 

Can Spinal Muscular Atrophy Be Treated?

There is currently no cure for spinal muscular atrophy. As of now, treatments for SMA include managing symptoms and trying to prevent complications. For example, physical therapy may help slow the progression of muscle weakness.

Talk to Your Doctor About Spinal Muscular Atrophy Testing

Genetic carrier screening allows parents-to-be to understand their risk of passing on a mutated gene associated with a genetic condition to their child. If you’re interested in learning more about carrier screening for your future pregnancy, talk to your doctor.