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Healthcare Professionals

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Do you suspect hypotonia? This could be SMA, especially in a child who appears socially engaging and responsive. Be sure to rule out an SMA diagnosis immediately and do not delay. It is critical to identify and treat SMA emergently before the onset of further, irreversible motor damage.

The early diagnosis and the early treatment of SMA is absolutely essential to maximize a child’s health outcomes from this debilitating disease. Early treatment is often the difference between life and death, between extremely limited function and independent mobility.

Clinical Presentation of SMA by Type

SMA is categorized into subtypes based on age of onset and highest motor milestone achieved. The most common three types in children present as follows:


Symptom onset <6 months

  • Progressive hypotonia
  • Typical supine position is bent elbows and frog legs
  • Difficulty lifting extremities against gravity
  • Rapid paradoxical breathing or belly breathing
  • Bell-shaped chest
  • Poor head control / head lag
  • Bulbar weakness / dysphagia
  • Developmental regression
  • Never sits

Symptom onset 6 to 18 months

  • Progressive hypotonia
  • Difficulty lifting extremities against gravity
  • Possible paradoxical breathing or belly breathing
  • Possible bell-shaped chest
  • Tongue fasciculations
  • Absent deep tendon reflexes
  • Developmental regression
  • Delayed sitting and never walks unaided

Type 3
Symptom onset 1.5 to 10 years

  • Progressive hypotonia
  • Muscle tremor
  • Fatigue with exertion and frequent falls
  • Gower’s sign, Trendelenburg gait, hyperlordosis, and foot overpronation
  • Developmental regression
  • Delayed walking

Multiple effective treatments approved by the U.S. Food and Drug Administration (FDA) have dramatically changed the natural history of SMA. Promptly evaluate for SMA upon suspicion in clinic. Genetic testing is required to confirm SMA. Rapid response can save and dramatically improve a child’s life.

SMArt Moves Professionals’ Proof Points

Historically, healthcare professionals have been slow to refer a child for concerns about motor delays. In part, SMA is a rare disease and an SMA diagnosis was once perceived as dismal, prior to the availability of the first FDA-approved treatment for SMA in 2016. There are now multiple FDA-approved treatments for SMA, and additional treatments in development or in clinical trials. With the availability of these life-altering SMA treatments, the timing of administration is crucial.

  • Early treatment, within the first few months after exhibiting SMA symptoms, will show significant improvements. SMA treatment started after that crucial early window can still result in benefit, but their health outcomes and improvements may not be as great compared to children treated at the earliest onset of the disease.
  • Most children are not being diagnosed as early as possible, even when presenting tell-tale symptoms.
  • Most parents instinctually know something is wrong but are not exactly sure if these developmental delays are serious, or they may be in denial. If a healthcare professional initially dismisses concerns, parents are generally not prepared to prompt further conversations to drive a thorough evaluation.
  • Doctors often suggest a “wait-and-see” approach in response to a child’s motor developmental delays and may not be attune to the nuances of diagnosing SMA. They may not know the urgency required to maximize the effectiveness of available SMA treatment.

We hope this information will help you make informed decisions about diagnosing SMA and change the outcome for so many young children and their families.


Finkel RS, Mercuri E, Darras BT, et al. Nusinersen versus Sham Control in Infantile-Onset Spinal Muscular Atrophy. N Engl J Med. 2017;377(18):1723–1732. doi:10.1056/NEJMoa1702752

Mendell JR, Al-Zaidy S, Shell R, et al. Single-Dose Gene-Replacement Therapy for Spinal Muscular Atrophy. N Engl J Med. 2017;377(18):1713–1722. doi:10.1056/NEJMoa1706198

Mercuri E, Darras BT, Chiriboga CA, et al. Nusinersen versus Sham Control in Later-Onset Spinal Muscular Atrophy. N Engl J Med. 2018;378(7):625–635. doi:10.1056/NEJMoa1710504

De Vivo DC, Bertini E, Swoboda KJ, et al. Nusinersen initiated in infants during the presymptomatic stage of spinal muscular atrophy: Interim efficacy and safety results from the Phase 2 NURTURE study. Neuromuscul Disord. 2019;29(11):842–856. doi:10.1016/j.nmd.2019.09.007

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