In addition, Qu et al. reported that a distribution for SMN2 copy numbers in 232 Chinese SMA patients of 4 SMN2 copies in 13 patients (5.6%), 3 copies in 153(65.9%), 2 copies in 66(28.5%) and no patients having only 0 or 1 copy of SMN2 [8]. Here, SMN2 is linked to proximal spinal muscular atrophy.