Frank, an SMA parent, describes the genetics of SMA.
So, my understanding on how SMA works is that the disease itself is caused by a lack of a protein called SMN and the reason the body is lacking this protein is because there's a deletion of a gene called SMN1. And a certain amount of protein is needed to live. For Maeve to exist, there's a certain amount of protein to exist then just by nature, nature has given SMA patients a backup gene called SMN2. Now you would think that SMN2 is producing the same protein and, you know, that it would compensate for the lack of the SMN1 gene, but it doesn't because the SMN2 gene in itself creates a low functioning protein due to a problem in its genetic makeup. And it produces something like 10% of the protein that would normally be required for a normal individual.