3.
SMA患儿和健康儿童SMN2拷贝数分布情况比较[例（%）]
| SMN2拷贝数 | SMA患儿 | 健康儿童 | P值 |
| 0 | 0 | 3(6) | |
| 1 | 0 | 18(36) | |
| 2 | 11(24) | 28(56) | < 0.001 |
| 3 | 26(58) | 1(2) | |
| 4 | 8(18) | 0 | |
| 合计 | 45(100) | 50(100) |
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