SMN1 and SMN2 quantification was undertaken to investigate the genotype-phenotype relationship.RESULTS: Two novel point mutations were identified in exon 3 of SMN1 (p.Tyr130Cys and p.Tyr130His) in the highly conserved Tudor domain of the Smn protein.CONCLUSIONS: The genetic basis of SMA in the rare cases of compound heterozygous carriers of SMN1 deletions is complex.