Spinal muscular atrophy (SMA) is a genetic disorder characterized by progressive muscle loss. SMA is caused by a deficiency of the survival of motor neuron (SMN) protein. Nusinersen increases SMN expression by modifying the alternative splicing of the SMN2 gene.

Intrathecal nusinersen has been recently approved for the treatment of SMA. In Poland, children with different SMA stages received nusinersen before the drug approval within an expanded access program (EAP).

In this multicentre, prospective, open-label study, we included patients with infantile-onset SMA type 1 who received nusinersen within the EAP from February 2017 to September 2018. Standardized assessments included the Children's Hospital of Philadelphia Infant Test of Neuromuscular Disorders (CHOP INTEND), which was done at baseline and after 12 months of treatment.

Data from 29 patients with SMA type 1 (mean age, 30 months; range, 2-256 months) were available. On average, the CHOP INTEND score improved by 6,3 points,   by 2 points, in children with two SMN2 copies (n = 21),  and by 12.3 points, in children with ≥3 SMN2 copies (n = 8).

Untreated SMA leads to progressive muscle weakness, but intrathecal nusinersen given for 12 months improved motor function in children with different stages of SMA type 1.