source: Muscular Dystrophy Australia
Spinal muscular atrophy (SMA) is a genetic condition which affects the nerves that control muscle movement – the motor neurons.
It is named ‘spinal’ because most of the motor neurons are located in the spinal cord. ‘Muscular’ is in the name because it primary affects the muscles which don’t receive signals from the motor neurons. ‘Atrophy’ is the medical term for wasting away or getting smaller, which is what generally happens to muscles when they’re not active.
There is wide variability in age of onset, symptoms and rate of progression of SMA and it is often classified into types 1 to 4 based on the physical milestones achieved. Please see the document ‘Spinal Muscular Atrophy – an overview’ for a brief description of the different types.
Babies usually start to show symptoms of SMA type 2 between the ages of seven and 18 months. They are able to eventually sit unsupported but are usually not able to stand without support. Despite a set pattern of weakness, each person is different in the extent to which they are affected. Some children with SMA type 2 live well into adulthood and others are weaker and have shorter lives.