Rs4916

This SNP is discussed in the discussion of spinal muscular atrophy (SMA); it is a SNP theoretically found in exon 7 of the SMN1 gene.

In a world with perfect analytic tests, there would be 3 possible genotypes most likely to arise from this SNP: (-;-), (-;C), and (C;C), indicated spinal muscular atrophy patients, carriers for SMA, and non-carriers, respectively.

However, due to the presence of identical flanking sequences to either side of this location in the genome for the near identical gene SMN2, an imperfect test can yield a (T;T) genotype for this SNP, which is really just a read of the SMN2 gene sequence at this location.

Test that determine the ratio of what could be called rs4916(C) to rs4916(T) "alleles" may be possible to determine dosage ratio between SMN1 and SMN2. Unaffected individuals should have a 1:1 ratio of (C):(T) "alleles", SMA carriers should have a 1:2 ratio of (C):(T) "alleles", and 95% of SMA patients should show have only (T) "alleles" (without any (C) signal).