Molecular characterization and copy number of SMN1 , SMN2 and NAIP in Chinese patients with spinal muscular atrophy and unrelated healthy controls

Background Spinal muscular atrophy (SMA) is caused by SMN1 dysfunction, and the copy number of SMN2 and NAIP can modify the phenotype of SMA. The aim of this study was to analyze the copy numbers and gene structures of SMA-related genes in Chinese SMA patients and unrelated healthy controls. Methods Forty-two Chinese SMA patients and two hundred and twelve unrelated healthy Chinese individuals were enrolled in our study. The copy numbers and gene structures of SMA-related genes were measured by MLPA assay. Results We identified a homozygous deletion of SMN1 in exons 7 and 8 in 37 of 42 patients (88.1%); the other 5 SMA patients (11.9%) had a single copy of SMN1 exon 8. The proportions of the 212 unrelated healthy controls with different copy numbers for the normal SMN1 gene were 1 copy in 4 individuals (1.9%), 2 copies in 203 (95.7%) and 3 copies in 5 (2.4%). Three hybrid SMN genes and five genes that lack partial sequences were found in SMA patients and healthy controls. Distributions of copy numbers for normal SMN2 and NAIP were significantly different ( P < 0.001) in people with and without SMA. Conclusion The copy numbers and gene structures of SMA-related genes were different in Chinese SMA patients and healthy controls.