Table 2.
Disease characteristics, all individuals with SMA types I, II, and III
| Characteristics | 2018 Survey | 2017 Survey | ||||
| Type I | Type II | Type III | Type I | Type II | Type III | |
| (n = 268) | (n = 290) | (n = 173) | (n = 213) | (n = 270) | (n = 187) | |
| Age at symptom onset | ||||||
| N | 258 | 272 | 159 | |||
| Mean (SD), months | 2.6 (3.9) | 10.2 (10.4) | 39.4 (70.6) | NC | NC | NC |
| Median (range), months | 2 (0–49) | 9 (0–160) | 18 (0–680) | NC | NC | NC |
| Age at diagnosis | ||||||
| N | 263 | 280 | 167 | 203 | 243 | 167 |
| Mean (SD), months | 5.2 (10.7) | 22.9 (33.1) | 114.4 (119.8) | 4.9 (9.6) | 21.7 (36.9) | 107.5 (126.2) |
| Median (range), months*, † | 4 | 16 | 59 | 4 | 16 | 46 |
| (–6 to 128) | (–7 to 310) | (–6 to 587) | (–9 to 126) | (–6 to 520) | (–5 to 587) | |
| Diagnostic delay‡ | ||||||
| N | 226 | 242 | 138 | |||
| Mean (SD), months | 5.7 (33.4) | 15.9 (39.7) | 89.4 (111.8) | NC | NC | NC |
| Median (range), months | 2 (0–437) | 7 (0–329) | 37 (0–547) | NC | NC | NC |
| SMN2 copy number, n (%) | ||||||
| 1 copy | 19 (7.1) | 3 (1.0) | 1 (0.6) | 14 (6.6) | 6 (2.2) | 1 (0.5) |
| 2 copies | 117 (43.7) | 27 (9.3) | 10 (5.8) | 85 (39.9) | 16 (5.9) | 5 (2.7) |
| 3 copies | 16 (6.0) | 112 (38.6) | 36 (20.8) | 7 (3.3) | 83 (30.7) | 29 (15.5) |
| 4 copies | 0 | 5 (1.7) | 39 (22.5) | 1 (0.5) | 0 | 19 (10.2) |
| 5 or more copies | 1 (0.4) | 0 | 6 (3.5) | 0 | 1 (0.4) | 3 (1.6) |
| Don’t know/missing | 115 (42.9) | 143 (49.3) | 81 (46.8) | 106 (49.8) | 164 (60.7) | 130 (69.5) |
NC, not collected; SMA, spinal muscular atrophy. *Excluded values of <-9 months. †Negative values indicate diagnosis before birth. ‡Diagnostic delay = age at diagnosis minus age at symptom onset. If diagnostic delay was negative (child started to show symptoms after receiving a diagnosis), the negative value was edited to “0” to indicate no diagnostic delay.