Humans have two forms of SMN protein-coding genes located on chromosome 5q13, identified as SMN1 and SMN2. SMN1 and SMN2 are almost identical. However, 70%–95% less of the full-length SMN protein is produced by SMN2 than by SMN1. The reason for SMN2 being unable to produce sufficient amount of full-length SMN protein is a C–T replacement inside exon 7 that is not present in SMN1.
Researcher have developed a method allowing the evaluation of the functional SMN protein in PBCs using imaging flow cytometry. The expression of SMN protein in CD3+, CD19+, and CD33++ cells obtained from SMA patients, was significantly reduced compared with that in cells from control subjects. Notably, in spot analysis of CD33++ cells, the intensities of SMN spots were significantly reduced in SMA subjects, when compared with that in controls. Moreover, the defined SMN spots were co-localized with Smith core proteins.
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