Spinal muscular atrophy (SMA) is a rare genetic condition (affects between 10,000-25,000 kids and adults). SMA is characterized by weak muscles as a result of non-functional nerve cells in the spinal cord and brainstem. In addition to muscle weakness, those with SMA may have limited mobility, breathing trouble, problems eating and swallowing, and delayed motor skills. These challenges make diagnosing SMA at the earliest possible age very important.
Diagnosing SMA
SMA is often challenging to diagnose because symptoms may overlap with other neuromuscular conditions. Specific tests can be done to confirm whether the symptoms are due to SMA:
- Blood test to identify mutations in the SMN1 gene
- Electromyography (EMG): to test electrical activity in muscles
- Creatine kinase test: to rule out a different neuromuscular disease
SMA is classified into four categories:
- Type I: Also known as Werdnig-Hoffmann disease or infantile-onset SMA, symptoms become noticeable within the first six months of age. Symptoms are quite severe and include difficulty breathing and swallowing, reduced ability to use limbs, lack of reflexes. As they grow older, the children may develop a curved spine or other skeletal disorders that can prevent them from sitting up or standing. Most children die within the first two years of life from respiratory failure.
- Type II: Symptoms are noticed between 6-18 months of age. These children can sit up but need assistance with standing. They too face respiratory issues. Treatment can improve motor function in type II patients. Life expectancy among these children is into adolescence or young adulthood.
- Type III: Symptoms are usually noticed a year and a half (18 months) after birth. The first symptoms may appear are children having difficulty walking, running, climbing stairs, or getting up from a chair. They may develop a curved spine and shortening of muscles or tendons around joints, which can affect free movement of joints. Respiratory infections are a potential complication as well, but children with type III SMA have a normal lifespan.
- Type IV: Symptoms develop after 21 years of age.
Challenges Diagnosing SMA
According to Emma Ciafaloni, MD, Professor of Neurology and Pediatrics at the University of Rochester Medical Center, adult-onset or type IV SMA, is often misdiagnosed as multiple sclerosis, limb-girdle muscular dystrophy, or some other neurological disorder. She said that babies with type I SMA often face an average of 3-4 months of delayed diagnosis after initial symptoms. Those with type 2 and 3 face even longer delays—type 3 SMA may be diagnosed almost four years post symptom recognition.
A series of focus groups conducted with SMA patients, caregivers, and clinicians identified several factors that can cause diagnostic delays:
- Lack of awareness and knowledge about SMA among primary care clinicians and some neurologists
- Pediatricians dismissed symptoms of motor symptom deficits in babies as being ‘delayed development’
- Differential diagnosis (using a combination of health history and physical examination to arrive at a diagnosis): children often had other chronic illnesses that masked SMA symptoms. Others had their symptoms attributed to side effects of medications they were taking.
Poor access to the tools for Diagnosing SMA
A relatively quick diagnosis was only possible for those who lived near a medical center that had SMA specialists. Patients who lived far from large medical centers had to endure several weeks of testing and waiting for results. Parents had to find information on their own to have their child referred to a specialist for further evaluation.
Newborn screening (NBS) for SMA symptoms could help overcome some of these issues with delayed diagnosis. Some parents felt NBS could:
- Shorten the time to accurate diagnosis
- Prepare them psychologically
- Help find support groups
- Ensure there’s adequate insurance coverage
- Prepare for improving their child’s quality of life
St. Mary’s Healthcare System for Children has developed a diagnostic tool kit for SMA that could be a useful tool for early diagnosis. Like most conditions, early detection is important.
Additional Resources:
Newborn Screening for SMA by CureSMA
What Wouldn’t You Do Right Now for Your Child with a Rare Disease? by Kate Pecora
The June 5, 2020 Episode of the Patients Rising Podcast: https://www.patientsrisingpodcast.org/denied-access-to-treatment/
Surabhi Dangi-Garimella, Ph.D. is a biologist with academic research experience, who brings her skills and knowledge to the health care communications world. She provides writing and strategic support to non-profit groups via her consultancy, SDG AdvoHealth, LLC.