A very small percentage of patients with a phenotype compatible with spinal muscular atrophy are found not to have homozygous deletions or point mutations in the SMN1 gene (non-5q SMA). Clinicians and biologists from five French Neuromuscular Reference Centres shared their experience in this field:
- 24 patients with non-5q SMA from nine families were documented clinically and electrophysiologically,
- additional genetic studies were carried out (large panel of genes, whole exome, whole genome depending on the case),
- in 10 of them, including nine index cases, variants considered pathological were identified in the DYNC1H1, BICD2 and ASAH1 genes.
The authors highlight the relatively low diagnostic yield (39%).