SMN2 and proximal spinal muscular atrophy: In our pediatric validation cohort, 24 SMA patients were included with an age range between 3 weeks and 8 years at start of treatment: 33% (n = 8) had two SMN2 copies, 42% (n = 10) had three SMN2 copies, and 21% (n = 5) had four SMN2 copies.