A study of data from 268 patients with 4 copies of the SMN2 gene from the SMArtCARE registry showed :
- an average age of first symptoms of 6.4 years,
- 55% of patients present their first symptoms before the age of 3 and almost 95% are symptomatic by the age of 18,
- 3% have never acquired the ability to sit unaided, 13% to walk unaided, and 33% have lost the ability to walk independently,
- 43% have developed scoliosis, but only a quarter have had spinal surgery,
- 6.3% are on non-invasive ventilation and 1.1% are tube-fed,
It is worth noting, however, that patients with few or no symptoms are not included in this register.
The authors suggest that not all copies of SMN2 may be capable of producing the SMN protein, highlighting the possibility that one or two copies may be defective. This hypothesis remains to be confirmed.
