On the other hand, in SMA type I, the distributions of SMN2 copy number were as follows: 1 (46.7%), 2 (46.7%), and 3 (6.7%), whereas distributions were 2 (20%), 3 (60%), and 4 (20%) in SMA type II (Table 4). Here, SMN2 is linked to spinal muscular atrophy, type II.