The SMN1 Gene
Most people have two copies of the survival motor neuron 1 (SMN1) gene – one inherited from each parent. These genes contain the information needed to make the SMN protein that keeps the lower motor neurons in the spinal cord healthy. People with 5q SMA have a fault or mutation in both copies of their SMN1 gene which means they are unable to produce the SMN protein they need. Without this, the lower motor neurons deteriorate which restricts their ability to carry electrical signals from the brain to move the muscles that are affected in SMA. This causes muscle weakness which can affect movement, breathing and swallowing.
The SMN1 gene is on the fifth chromosome in the region labelled as ‘q’ which is why the main types of SMA are often referred to as 5q SMA.