Before drug treatments (also sometimes known as ‘disease-modifying’ treatments) started to be developed and tested for SMA, clinicians and researchers gathered information about what impact parents / carers might expect the condition to have on their child. This was called the ‘natural history’ of the condition and was different for each ‘Type’ of SMA.

In SMA Type 1, symptoms of muscle weakness usually begin between 0 and 6 months of age. In general, the earlier the onset of symptoms, the more severe the condition. Sometimes SMA can affect babies even before birth; this may be called SMA Type 0.

In the natural history of SMA Type 1, each child is affected differently but, in general, babies are:

• bright, alert and responsive; their intelligence is not affected
• able to smile and frown as their facial muscles are not severely affected
• often described as ‘floppy’ babies due to their low muscle tone (hypotonia) and severe muscle weakness
• unable to support or lift their head due to their weak neck muscles
• unable to sit unsupported (‘non-sitters’) and have difficulty rolling over
• able to move their hands and fingers but have difficulty lifting their arms and legs

In the natural history of SMA Type 1, children have:

• weak breathing muscles, which can cause a weak cry and difficulties with breathing and coughing
• an increased chance of chest infections, which can be life-threatening
• difficulty swallowing their saliva and other secretions, which may make them sound chesty or make them cough
• difficulties feeding and gaining weight
• an increased risk of fluids or food passing into their lungs (aspiration), which can cause choking and, sometimes, chest infections or pneumonia

Before 2007, without intervention for breathing difficulties, most children diagnosed with SMA Type 1 were expected to live for less than two years¹. The November 2017 ‘International Standards of Care for SMA’ refers to evidence that suggests that since more proactive managements were introduced in 2007, children were living longer^2,3.

Global clinical trials and follow-up studies of possible drug treatments for those who have SMA Type 1 had tended to focus on their impact on motor milestones and survival. There is more understanding now of the importance of respiratory outcomes, and the value of other outcomes that impact on a child’s quality of life, such as the development of: swallowing, feeding / eating; verbal communication; muscle support of spine and hips; fine motor skills and fatigue levels.

• Changing outcomes

In the UK, most children now living with SMA Type 1 will have started ongoing Spinraza™ / Nusinersen treatment (from as early as 2018) or, more recently, received the one-off gene therapy Zolgensma™ / Onasemnogene abeparvovec or ongoing Evrysdi™ / Risdiplam doses. These treatments have been life-saving. Most treated children have gained strength, movement and better health. Though many do have complex care needs⁴, with appropriate support, we are now seeing children joining mainstream school.

How SMA will impact the health and daily life of a treated child living with SMA Type 1 today – and how the natural history of their condition may change – is very individual. It will be influenced by factors including the age at which symptoms first appeared, the severity of symptoms, how early any treatment was started, and their individual response to treatment.

Though they can alleviate some symptoms, none of the drug treatments are a cure. They must be combined with the best supportive care and management of symptoms to ensure the best possible outcomes for each individual child.

• Drug Treatments for Children in England who have SMA >
• Looking after your child who has had a recent diagnosis of SMA Type 1 – for parents and carers >
• Living With SMA – information and ideas for daily living >
• International Standards of Care for SMA >
• What is 5q Spinal Muscular Atrophy? >
• The Genetics of 5q SMA >
• Treatments & Research >
• Drug Treatments for Adults in England who have SMA >

1. Montes J et al. (2009) Clinical outcome measures in spinal muscular atrophy, J Child Neurol 24: 968-978.
2. A Guide to the 2017 International Standards of Care for SMA. Available at: smauk.org.uk/international-standards-of-care-for-sma (Accessed: 14th May 2021)
3. Mercuri E et al. (2018) Diagnosis and management of spinal muscular atrophy: Part 1: recommendations for diagnosis, rehabilitation, orthopedic and nutritional care. Neuromuscul Disord 28: 103-115.
4. Mercuri E et al. (2020) Spinal muscular atrophy – insights and challenges in the treatment era. Nat Rev Neurol 16: 706-715.