Spinal muscular atrophy (SMA) is a degenerative motor neuron disease which results in paralysis of very varying age and severity. There are four types depending on the age of onset and the best motor function achieved. Infants with type I are by far the most common (50 to 60%) but also the most severely affected. The natural history of the other three types is less well known, which represents a real disincentive to the evaluation of innovative therapies now on the market.
In an article published in October 2020, an Anglo-Italian-American consortium dedicated to SMA was particularly interested in the respiratory aspects of this natural history in 348 patients with type II and 89 with type III still walking, none among them not benefiting from innovative therapy. The study of the evolution of functional respiratory tests coupled with either global functional scores, such as HFMS, or targeted to the upper limb, such as RULM, allowed the authors to establish degradation curves and slopes in these subgroups of patients and to note some initial evolutionary differences between them. In contrast, the curves of deterioration in respiratory function become parallel again and remain rather stable from the age of thirteen. These data will be very useful in building efficacy criteria for future clinical trials.
