In general, each corresponds to the copy number of the SMN2 gene, which produces a small fraction (~10%) of functional SMN protein, essential to the survival of motor neurons, compared with SMN1.

SMA, a rare, genetic neuromuscular disease caused by a lack of a functional SMN1 gene, results in the irreversible ... with SMA with three copies of SMN2 aged 6 months to less than 60 months.

or patients with 5q SMA with a bi-allelic mutation in SMN1 and up to three copies of the SMN2 gene. Zolgensma is the world’s most expensive drug, with a price tag of more than $2.1 million per ...