SMN1 and proximal spinal muscular atrophy: The PNCR natural history cohort• A natural history study of 337 patients with any form of SMA followed at 3 large, tertiary medical centres• Contain data of patients with age of onset ≤6 months, bi-allelic deletion of SMN1 and 2 copies of SMN2• Retrospective and prospective enrolment data• Choice of primary endpoints