Cao et al. [11] found that in different copy numbers of SMN2, the distribution of type I and type 2/3 was significantly different (P < 0.001): when the copy number of SMN2 in parents was 1, 75% of SMA progenies were type 1 and 25% were type 2/3. The gene discussed is SMN2; the disease is proximal spinal muscular atrophy.