Department of Medical Genetics, Capital Institute of Pediatrics, Beijing, China.
BMC Med Genet. 2012 Sep 20;13:86. doi: 10.1186/1471-2350-13-86.
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.
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.
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.
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.
近端型脊髓性肌肉萎缩症（SMA）是一种常见的神经肌肉疾病，会导致儿童期死亡。大约 81%至 95%的 SMA 病例是由于生存运动神经元基因 1（SMN1）基因的纯合缺失或从 SMN1 到 SMN2 的基因转换所致。不到 5%的病例显示 SMN1 中罕见的细微突变。我们的目的是鉴定携带单个 SMN1 拷贝的中国 SMA 患者的细微突变。
我们检查了来自 13 个无关家庭的 14 名患者。多重连接依赖性探针扩增分析用于确定 SMN1 和 SMN2 的拷贝数。逆转录聚合酶链反应（RT-PCR）和克隆测序用于检测 SMN1 中的细微突变。使用定量 RT-PCR 测定 SMN 转录本水平。
在 12 名患者中鉴定出 6 种细微突变（p.Ser8LysfsX23、p.Glu134Lys、p.Leu228X、p.Ser230Leu、p.Tyr277Cys 和 p.Arg288Met）。p.Tyr277Cys 突变以前没有报道过。p.Ser8LysfsX23、p.Leu228X 和 p.Tyr277Cys 突变仅在中国 SMA 患者中报道过，前两种突变似乎更为常见。与健康携带者相比，携带 p.Ser8LysfsX23、p.Leu228X 或 p.Arg288Met 的患者全长 SMN1（fl-SMN1）转录本水平非常低。携带 p.Glu134Lys 或 p.Ser230Leu 的患者 fl-SMN1 转录本水平降低，但不显著。p.Arg288Met 突变患者的 SMN1 转录本几乎完全跳过外显子 7。
我们的研究揭示了中国 SMA 患者 SMN1 中细微突变的独特谱与其他种族不同。p.Arg288Met 错义突变可能影响 SMN1 中外显子 7 的正确剪接。对中国患者 SMN1 基因的突变分析可能有助于确定潜在的种族差异，并丰富 SMN1 细微突变数据库。
