For Patients: Understanding Spinal Muscular Atrophy (SMA)  image

For Patients: Understanding Spinal Muscular Atrophy (SMA) 

SMA Overview | SMA Screening | SMA for Patients 

Faculty 

Melissa Gibbons, MS, CGC 

Samone Masters, MS, CGC 

Tamar Ailenberg, MS, CHC, CCG 

Melissa Gibbons, a certified genetic counselor, is an associate professor in the Department of Pediatrics-Genetics and Metabolism at the University of Colorado School of Medicine and Children’s Hospital Colorado in Aurora, CO 

Samone Masters is the Supervising Genetic Counselor in the Department of Obstetrics and Gynecology at Jacobi Medical Center in Bronx, NY 

Tamar Ailenberg is a certified genetic counsellor with both the American Board of Genetic Counselors and the Canadian Association of Genetic Counsellors. She is a practicing genetic counselor in Ontario, Canada 

WHAT IS SMA? 

  • People with spinal muscular atrophy (SMA) have weakness and wasting in their muscles that worsens over time 
  • SMA occurs because affected people don’t make enough of an important protein called ‘survival motor neuron’ protein, or SMN protein for short  
    • This protein normally supports certain cells, called motor neurons, that send signals from the brain and spinal cord to control our movements 
    • Without working motor neurons, muscles do not receive the proper signal from the brain, causing the muscles to shrink and not work properly over time 
  • The age when signs or symptoms start and the severity of SMA can differ from person to person  
    • SMA may start in infancy but symptoms can occur throughout an individual’s life 
  • In general, the earlier a person develops symptoms, the more severe the condition tends to be, and fewer motor milestones are achieved 
  • The severity of SMA is variable and can be classified from Type 0 (most severe) to Type 4 (least severe)  
    • SMA Type 1 is the most common form of the disorder  
      • Infants cannot sit without help or control head movements, and have difficulty swallowing and breathing 
  • More and more, doctors are using the following categories for SMA based on which milestones have been reached  
    • Non-sitter 
    • Sitter 
    • Walker 

COMMONLY ASKED QUESTIONS: 

How Is SMA Passed Along in Families? 

  • The main gene associated with SMA is called SMN1, which stands for ‘survival motor neuron 1’  
    • SMN1 makes the majority of the SMN protein 
    • Most people have 2 copies of the SMN1 gene 
  • A ‘carrier’ of SMA is a person who has one non-working copy and one working copy of the SMN1 gene 
  • Those who have a diagnosis of SMA have 2 non-working SMN1 genes (neither copy in the pair are working) 

Note: Carriers of SMA will not have any health problems related to SMA because with one working copy of the gene, they make enough SMN protein to stay healthy. Carriers often do not know that they are carriers unless they undergo genetic testing 

  • If both parents are carriers of SMA, they have a 25% risk of having a baby with SMA 

Note: Although SMA is caused by having 2 ‘non-working’ SMN1 genes, the severity found in individuals can be different 

  • We also have ‘back-up’ genes called SMN2  
    • SMN2 genes also make a small amount of SMN protein, but they don’t produce as much of the protein as the SMN1 gene 
    • A person can have multiple copies of SMN2 
    • In general, if people with SMA have more copies of SMN2, they make more SMN protein, and if they have more protein, then SMA may be less severe 
    • The number of SMN2 copies an individual has can only be determined by genetic testing 

Why Am I Being Offered SMA Carrier Screening? 

  • Current guidelines recommend that all individuals who are pregnant or are considering pregnancy should be offered carrier screening for SMA  
    • Testing can happen once in a lifetime and does not need to be repeated 
  • These recommendations are made because it is common to be a carrier  
    • Approximately 1 in 50, or 2% of the population, are carriers of SMA 
    • SMA can be a very severe condition that can impact an individual’s life expectancy  
  • Couples who are at-risk of having a child with SMA may wish to educate themselves about options for their family that may include:  
    • Early diagnosis prenatally or at birth and prompt treatment 
    • Discussion regarding reproductive options 

What If I Do Not Have a Family History Of SMA? Do I Still Need a Genetic Screening Test? 

  • Carriers of SMA may not be aware of their carrier status as typically they have no symptoms nor family history of SMA 
  • Being a carrier can be passed along for generations without an affected individual within the family  
    • SMA can stay silent over many generations because this condition follows what we call an autosomal recessive inheritance pattern 
    • In the majority of cases, both parents must be carriers for a pregnancy/child to be affected  
    • If both parents are carriers, there is a 1 in 4 chance (25%) with each pregnancy that their child will have SMA 
  • If an individual is a known carrier and becomes pregnant with a new partner, it is important for the new partner to consider carrier screening to understand the risk for their child  
    • If the new partner is not a carrier, they are very unlikely to have a child with SMA 

Is SMA Carrier Screening During Pregnancy Required? 

  • No; genetic screening tests during pregnancy are optional and voluntary 
  • Not all couples wish to learn about potential risks to their current/future pregnancy 
  • It is fine to say ‘no’ to any genetic testing – the choice is always yours  
    • Just make sure to let your healthcare professional know of your decision to decline carrier screening 
  • In most states, the baby will be tested at birth for SMA by newborn screening  

What is Newborn Screening? 

  • Newborn screening is a series of tests performed in the first few days of life to evaluate newborns for many types of disorders 
  • The goal of newborn screening is to identify certain conditions (like SMA) in newborns to ensure that timely identification, intervention, and treatment can occur in infants that may appear healthy at birth 
  • Newborn screening is performed on infants born within the United States in the first 24 to 48 hours of life  
  • Although newborn screening includes a hearing and an oxygen test, many disorders identified through newborn screening are found through a blood sample collected from the baby’s heel 

Is SMA included on Newborn Screening? 

  • Within the United States, the disorders that newborns are screened for differ by the state you live in  
    • At this time, not all states test for SMA 
  • If SMA is part of newborn screening, then regardless of whether the parents underwent carrier screening, their newborn will be screened for SMA  
  • Newborn screening for SMA is able to detect approximately 95% of SMA cases   
  • If your child’s newborn screening test finds SMA, you will be contacted to organize confirmatory testing and proper follow-up 

What Treatments are Available for SMA? 

Supportive Therapy 

  • Supportive care addresses symptoms of SMA rather than targeting the underlying cause of SMA itself 
  • Supportive care includes:  
    • Physical therapy 
    • Occupational therapy 
    • Respiratory therapy 
    • Nutrition support 

Medication 

  • Medical therapies are available to treat individuals with SMA in addition to supportive care  
    • Treated individuals can have a longer lifespan, improved motor milestone achievements, and are less likely to receive permanent breathing machines compared to untreated individuals 
    • Side effects are associated with all these medications and these should be discussed with experts who prescribe and administer these treatments 
  • Nusinersen (brand name: Spinraza)  
    • Helps the SMN2 gene to make more SMN protein, which increases the overall amount 
  • Onasemnogene abeparvovec-xioi (brand name: Zolgensma)  
    • Helps by inserting a working SMN gene into the body 
  • Risdiplam (brand name: Evrysdi)  
    • Helps the SMN2 gene to make more SMN protein  

Timing of Medical Therapy 

  • Regardless of what medication is chosen, it is important to begin treatment as early as possible 
  • Early treatment helps prevent irreversible loss of motor neurons, muscle atrophy, and therefore halts or slows the disease progression 

KEY POINTS: 

  • SMA is a genetic disorder that causes serious progressive muscle weakness that occurs when a child inherits two non-working copies of the SMN1 gene 
  • Carrier testing is voluntary but may provide information helpful to those making reproductive decisions for their family 
  • Although approximately 1 in 50 people are carriers of SMA, most are not aware of their carrier status  
  • Treatments can help stop the progression of SMA 

Learn More! 

Check to see if your state includes SMA on their Newborn Screening 

MedlinePlus: Spinal Muscular Atrophy 

NORD: Spinal Muscular Atrophy 

NIH – GARD: Spinal Muscular Atrophy 

FDA: Zolgensma   

FDA: Evrysdi  

FDA: Spinraza  

Faculty Disclosures 

Melissa Gibbons has participated in Taysha Gene Therapy Advisory Board 

Samone Masters has no relevant financial relationships to disclose 

Tamar Ailenberg has no relevant financial relationships to disclose  

Commercial Support 

8/2023 US-UNB23-0032