Trinucleotide insertion in the SMN2 promoter may not be related to the clinical phenotype of SMA

Patient A was judged to be an exceptional case of SMA, because the GCC insertion polymorphism rarely exists in SMN1-deleted SMA patients. The GCC insertion polymorphism did not enhance the transcriptional efficiency of SMN2. Thus, this GCC insertion polymorphism in the SMN2 promoter may not be associated with the milder phenotype of the patient. Patient A suggests that there are other unknown factors modifying the clinical phenotype of SMA.