The ‘Natural History’ of SMA

Before the new drugs for 5q SMA were developed, clinicians studied the effects of SMA on people. This is called the ‘natural history’ of the condition.

This led to 5q SMA being divided into four main Types of SMA: Types 1, 2, 3, and 4. Sometimes a baby is affected before birth; this is called Type 0.

These ‘Types’ of SMA are based on the age that symptoms begin, and what physical milestones (e.g. sitting, standing, walking) are achieved. Clinicians agreed that there could be variation both within and between ‘Types’.

What would the ‘natural history’ of my child’s / my SMA look like?

To try to answer this question, a specialist clinician will examine any child or adult with suspected SMA.

They will also consider:

• the age of the child or adult when the SMN1 gene deletion test confirmed SMA
• any symptoms of SMA and when these first started
• how many SMN2 gene copies the test result showed
• any family history of SMA

They will refer to this summary:

Clinical classification of SMA subtypes according to onset, milestones achieved, and clinical presentation. Typically associated SMN2 copy numbers are shown. Figure taken with permission from Schorling D et al. (2019) Advances in Treatment of Spinal Muscular Atrophy – New Phenotypes, New Challenges, New Implications for Care J Neuromuscul Dis 7: 1-13, under the CC BY-NC 4.0 licence.