SMN1 and proximal spinal muscular atrophy: The mean age (shown with standard deviation) of confirmed genetic diagnosis of SMA was 0.4 months for SMA type 0; 3.2 ± 2.4 months (range 0.1–8 months) for SMA I; 18.8 ± 6.7 months (range 11–35 months) for SMA II; 13.4 ± 15.2 years (range 2–54 years) for SMA III; and 43 years for SMA IV.