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Signs and symptoms of SMA

Individuals with SMA experience a range of symptoms, but the most common signs include progressive muscle weakness, floppiness, and muscle wasting. Measuring milestones is an important part of monitoring child development.

Symptoms of SMA are not easily recognised

SMA is classified into different types1,2

  • Single spectrum of disease
  • Classification into types helps to understand the spectrum3
  • SMA is divided into four types based on the age of onset and maximum functional ability achieved4
  • Most common types: 1, 2 & 35
  • Severity can also range within each type, and many individuals (up to 25%) cannot be classified into a precise type4

Signs of developmental delay

SMA is often first suspected by a parent who may notice that their child is not meeting typical developmental milestones for their age, such as holding their head up, rolling over or sitting up independently.

All babies develop at their own pace; the World Health Organization (WHO) suggests most healthy children will achieve large body motor milestones within the following timeframes:

Adapted from WHO Multicentre Growth Reference Study Group.6

Milestone definitions7

Sitting without support:

Child sits up straight with the head erect for at least 10 seconds. Child does not use arms or hands to balance body or support position.

Standing with assistance:

Child stands in upright position on both feet, holding onto a stable object (e.g. furniture) with both hands without leaning on it. The body does not touch the stable object, and the legs support most of the body weight. Child thus stands with assistance for at least 10 seconds.

Hand and knees crawling:

Child alternately moves forward or backward on hands and knees. The stomach does not touch the supporting surface. There are continuous and consecutive movements, at least three in a row.

Waking with assistance:

Child is in upright position with the back straight. Child makes sideways or forward steps by holding onto a stable object (e.g. furniture) with one or both hands. One leg moves forward while the other supports part of the body weight. Child takes at least five steps in this manner.

Standing alone:

Child stands in upright position on both feet (not on the toes) with the back straight. The legs support 100% of the child’s weight. There is no contact with a person or object. Child stands alone for at least 10 seconds.

Walking alone:

Child takes at least five steps independently in upright position with the back straight. One leg moves forward while the other supports most of the body weight. There is no contact with a person or object.

Learn more about WHO motor milestones here

If you are concerned about your child’s development, please speak to your doctor or nurse as soon as possible as this may lead to an earlier diagnosis of SMA, which can improve outcomes.

Tracking growth and development

Measuring milestones allows parents, carers and health professionals to assess a child’s physical growth and development as they age. Download the milestone checklist8 below and tell your doctor or nurse if you notice any signs of possible
developmental delay.

Download the checklist
References
  1. Munsat TL and Davies KE. Neuromuscul Disord 1992; 2(5-6): 423–8.
  2. Faravelli I et al. Nat Rev Neurol 2015; 11(6): 351–9.
  3. D’Amico A et al. Orphanet J Rare Dis 2011; 6: 71.
  4. Kolb S and Kissel J. Neurol Clin 2015; 33: 831–46.
  5. Jones C et al. Systematic review of incidence and prevalence of spinal muscular atrophy (SMA). Presented at the European Paediatric Neurology Society Congress, Vienna, Austria; May 27–30, 2015. Poster PP09.1-2352.
  6. WHO Multicentre Growth Reference Study Group. Acta Pædiatrica 2006; Suppl 450: 86–95.
  7. Wijnhoven TMA et al. Food Nutr Bull 2004; 25 Suppl 1: S37–45.
  8. CDC Milestone Checklist. Available at https://www.cdc.gov/ncbddd/actearly/pdf/checklists/Checklists-with-Tips_Reader_508.pdf (accessed February 2020).