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Background  Proximal spinal muscular atrophy (SMA) is a common neuromuscular disorder resulting in death during childhood. Around 81 ~ 95% of SMA cases are a result of homozygous deletions of survival motor neuron gene 1 ( SMN1 ) gene or gene conversions from  SMN1  to  SMN2 . Less than 5% of cases showed rare subtle mutations in  SMN1 . Our aim was to identify subtle mutations in Chinese SMA patients carrying a single  SMN1  copy.    Methods  We examined 14 patients from 13 unrelated families. Multiplex ligation-dependent probe amplification analysis was carried out to determine the copy numbers of  SMN1  and  SMN2 . Reverse transcription polymerase chain reaction (RT-PCR) and clone sequencing were used to detect subtle mutations in  SMN1 .  SMN  transcript levels were determined using quantitative RT-PCR.    Results  Six subtle mutations (p.Ser8LysfsX23, p.Glu134Lys, p.Leu228X, p.Ser230Leu, p.Tyr277Cys, and p.Arg288Met) were identified in 12 patients. The p.Tyr277Cys mutation has not been reported previously. The p.Ser8LysfsX23, p.Leu228X, and p.Tyr277Cys mutations have only been reported in Chinese SMA patients and the first two mutations seem to be the common ones. Levels of full length  SMN1  (fl- SMN1)  transcripts were very low in patients carrying p.Ser8LysfsX23, p.Leu228X or p.Arg288Met compared with healthy carriers. In patients carrying p.Glu134Lys or p.Ser230Leu, levels of fl- SMN1  transcripts were reduced but not significant. The  SMN1  transcript almost skipped exon 7 entirely in patients with the p.Arg288Met mutation.    Conclusions  Our study reveals a distinct spectrum of subtle mutations in  SMN1  of Chinese SMA patients from that of other ethnicities. The p.Arg288Met missense mutation possibly influences the correct splicing of exon 7 in  SMN1 . Mutation analysis of the  SMN1  gene in Chinese patients may contribute to the identification of potential ethnic differences and enrich the  SMN1  subtle mutation database.

Subtle mutations in the SMN1 gene in Chinese patients with SMA: p.Arg288Met mutation causing SMN1 transcript exclusion of exon7