Duchenne muscular dystrophy (DMD) is characterized by muscle deficit with loss of walking around the age of 12 years. Becker muscular dystrophy (BMD) is less severe: walking is preserved until the age of 16, or even is never lost. Both are linked to defects in the DMD gene which encodes dystrophin, a protein whose quantity is closely related to the severity of the phenotype.
A French team from the FILNEMUS network sought to determine the effects of a small amount of dystrophin by analyzing data from 90 patients with a mutation in the DMD gene, collected in the UMD-DMD France database. Three groups were formed according to the amount of dystrophin:
- no detectable dystrophin, 74% of whom developed DMD;
- less than 5% dystrophin, of which 61% developed BMD;
- more than 5% dystrophin, of which 57% have developed BMD and 71% are still walking.
The authors showed significantly milder symptoms in the group with less than 5% dystrophin than in the group without dystrophin, including those who have less than 0.5% of dystrophin. Apart from the age of onset and the ejection fraction of the left ventricle, the other parameters studied are significantly delayed: loss of walking, set up of spinal arthrodesis and death. These are encouraging data during these times when innovative therapies in development for dystrophinopathies aim to increase the amount of dystrophin.
