Individuals with SMA may experience symptoms differently, and the disease is divided into types based on age of onset and highest motor milestone achieved. There is also a range of severity within each type, and as many as 25% of individuals may not have a precise type.
UNABLE TO SIT
I (also known as Werdnig-Hoffmann
ABLE TO SIT INDEPENDENTLY
70% STILL LIVING AT AGE 25
II (also known as Dubowitz disease)
ABLE TO WALK
(“walkers,” although they may progressively lose this ability)
III (also known as Kugelberg-Welander disease)
Global Genes Project
Genetic and Rare Disease Network
National Organization for Rare Disorders
Parents may observe that their child is not reaching typical physical milestones for their age, such as the ability to hold their head up, to roll over, or to sit up independently. Swallowing or feeding may also become difficult, and children may lose the ability to swallow safely without choking or inhaling food into the lungs (aspiration).
While all babies develop at their own pace, the World Health Organization (WHO) offers the following general motor milestone guidelines as part of the Multicentre Growth Reference Study (MGRS):
Adapted from the WHO Multicentre Growth Reference Study.
Adapted from the Centers for Disease Control and Prevention Milestone Checklist.
Parents’ reports of their children’s gross motor development tend to be reliable. Sharing observations of potential motor delays with a doctor can help to determine an appropriate SMA care strategy.