Molecular diagnosis and genetic counseling for spinal muscular atrophy (SMA)

Spinal muscular atrophy (SMA) is a neuromuscular autosomal recessive disorder caused by bi-allelic pathogenic variants in the SMN1 gene. 95% of SMA patients have a SMN1 homozygous deletion. In the 5% remaining affected patients, a heterozygous SMN1 deletion is associated with an intragenic SMN1 rare inactivating pathogenic variant on the other allele. The clinical phenotype of SMA is heterogeneous and severity is inversely correlated with the number of SMN2 copies, a non-functional SMN1 copy. The development of new treatments leads to the generalization of carrier and newborn screening in many countries and new robust and low cost methods for large population-based screening have been developed. It is important that all diagnosed patients and relatives receive appropriate genetic counseling, taking into account the great complexity of SMA region to avoid pitfalls. © 2020 French Society of Pediatrics. Published by Elsevier Masson SAS. All rights reserved.