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. Type I SMA is the most severe form, characterized by a very rapid decline in muscle strength. Type II or III SMA starts later and progresses more slowly. So it is importance to have sensitive evaluation tools to detect a slight functional variation over a short period of time, the testing time rarely exceeding a two-year follow-up.
Nathis-SMA study
One of the objectives of the NatHis-SMA study, besides describing the natural history of type II and III SMA over two years, was to verify whether monitoring tools such as “Myotools”, which are being developed at the Institute of Myology, are sensitive enough to demonstrate functional or biological variations over this period. This study was carried out in 81 participants (53 with type II and 28 with type III), aged 2 to 30 years and not receiving basic treatment for SMA, between May 2015 and May 2018, in nine Reference Centres for Neuromuscular Diseases from France (including the Institute of Myology, Paris), Belgium and Germany.
Myotools in the spotlight
This natural history study, which may be one of the last given the increasing number of people with SMA receiving SMA treatment, has found:
- sufficiently sensitive and reliable detection of a significant decline in motor function over one or two years by the MFM32 and certain Myotools such as MyoGrip and MyoPinch which measure upper limb strength and ActiMyo which assesses upper limb activity;
- stability of the amount of SMN protein over two years; however, this measurement may be useful for assess the effectiveness of a treatment effective on the production of the protein;
- no significant change in vital capacity over two years.
Note that 32 participants left the study before the end to benefit from one of the new therapies recently authorized or to join a clinical trial. The authors conclude that the use of MFM32, MyoGrip, MyoPinch and ActiMyo could reduce the number of participants and the duration of future clinical trials.
