Compared to pre-treatment era data of pregnant SMA patients, worsening of muscle function in our patient and in the patient of Schön et al. [16] is partly due to the natural course of the disease without SMN restoring treatment, and partly to well-known accelerated worsening during pregnancy in SMA patients [7, 8, 16, 24]. This evidence concerns the gene SMN1 and proximal spinal muscular atrophy.