The genetic basis for the unusually high SMN1 copy number in the African American population is unknown. Previously published data have shown that individuals with higher copy numbers of SMN1 tend to have fewer copies of SMN2.22 It has been suggested that this correlation indicates that SMN2 may have converted to SMN1; however, the inverse may also be true. Alleles with multiple copies of SMN1 may be the ancestral form of the duplication, with conversion to SMN2 a more recent mutation event. An assessment of SMN2 copy number is currently underway to understand the SMN1/SMN2 correlation in this sample set.
