Patient & Health Education: What Is Spinal Muscular Atrophy?
If either you or your partner has a history of spinal muscular atrophy (SMA) in your family, then you likely have concerns about your pregnancy. One of the best ways to prepare yourself and your family for a genetic condition is to learn as much as you can about it.
So what is spinal muscular atrophy? What are the different types? How is the disorder inherited, and how can a carrier screening test from NTD Eurofins prepare you?
We’ll answer all your questions about the signs, symptoms, and causes of SMA so you can confidently plan for your family’s future.
What Is Spinal Muscular Atrophy?
According to the U.S. National Library of Medicine, spinal muscular atrophy is an inherited disorder where your muscles become weak to the point that they waste away. A lack of motor neurons, which are the nerve cells responsible for movement, causes SMA.
Eventually, the disorder leads to paralysis. Depending on the type of SMA disorder a person has, the age of onset can be anywhere from infancy to adulthood.
How Is Spinal Muscular Atrophy Inherited?
SMA occurs when a person has a mutation on both copies of the SMN1 gene, the gene responsible for proper motor function. In SMA, the gene mutation prevents the person from moving and walking properly.
A person inherits SMA from parents who each have one copy of the mutated gene. The parents do not show signs or symptoms of the disease, but as carriers, they can pass the mutation down to their offspring.
Sometimes, SMA occurs when a person has more than the usual two copies of the SMN2 genes – another gene responsible for motor neuron function. An extra copy of the SMN2 gene usually occurs not because of inheritance but a random error after fertilization.
What Are the Different Types of Spinal Muscular Atrophy?
According to the Muscular Dystrophy Association, five different types of SMA exist, depending on the way the SMN1 mutation occurs.
SMA Type 0
Physicians can detect SMA type O, the rarest and most severe form of the disorder, before birth. Babies move less in the womb and tend to be born with joint deformities. Their muscles are weak at birth. Sometimes their heart and respiratory muscles are also weak at birth, which can lead to heart and respiratory failure.
SMA Type I
SMA type I is also known as Werdnig-Hoffmann disease for the two neurologists who wrote about this particular form of spinal muscular atrophy. Type I is the most common type of SMA and, like type O, is severe.
Babies born with SMA type I have muscle weakness at birth or soon after. Children with SMA type I have trouble holding their heads up, sitting unassisted, swallowing, and feeding themselves. They also have breathing properly due to weak respiratory muscles, which can ultimately lead to respiratory failure.
SMA Type II
SMA type II, also known as Intermediate SMA, usually occurs in children between the ages of three and 15 months old. Children with type II tend to have muscle weakness in their lower limbs that prevent them from walking, as well as three copies of SMN2 genes.
They also have tremors and scoliosis – a curvature of the spine – and respiratory muscle weakness can lead to respiratory failure later in life.
SMA Type III
SMA type III usually has a later onset and occurs after early childhood. Type III is also known as Kugelberg-Welander disease and happens when a person has three or four copies of the SMN2 gene.
Someone with type III can walk without help at first, though climbing stairs is particularly difficult, but over time, they may lose mobility and need a wheelchair. People with type III have a normal life expectancy.
SMA Type IV
SMA type IV is rare, doesn’t generally affect people until early adulthood, and therefore has the highest life expectancy. People with type IV spinal muscular atrophy experience muscle weakness, tremors, and some breathing problems. However, breathing problems are mild and do not lead to respiratory failure.
What Screening Test Options Does NTD Eurofins Offer?
A carrier screening test is a great way to prepare yourself for the possibility of an inherited genetic condition. NTD Eurofins tests for inherited genetic disorders – like spinal muscular atrophy, among many others – with a simple blood draw. We can even test you before you become pregnant.
Most genetic conditions are rare, but knowledge is power. Genetic carrier screening tests give you the information you need to prepare for your family’s future.
Talk to your health care provider about which of NTD Eurofins’ genetic carrier screening tests are right for you.
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References
- Muscular Dystrophy Association. (n.d.). Spinal Muscular Atrophy. Muscular Dystrophy Association. https://www.mda.org/disease/spinal-muscular-atrophy/types
- U.S. National Library of Medicine. (2020). Spinal muscular atrophy. U.S. National Library of Medicine. https://ghr.nlm.nih.gov/condition/spinal-muscular-atrophy#
The information provided represents the general opinions of NTD Eurofins and is not intended to be used as specific advice for any one individual. Individuals should always consult with a physician to obtain specific advice and to receive answers to any and all questions or concerns related to health, wellness, pregnancy, and birth.