Harahap Nur Imma Fatimah, Takeuchi Atsuko, Yusoff Surini, Tominaga Koji, Okinaga Takeshi, Kitai Yukihiro, Takarada Toru, Kubo Yuji, Saito Kayoko, Sa'adah Nihayatus, Nurputra Dian Kesumapramudya, Nishimura Noriyuki, Saito Toshio, Nishio Hisahide
Department of Community Medicine and Social Healthcare Science, Kobe University Graduate School of Medicine, Kobe 650-0017, Japan.
Kobe Pharmaceutical University, Kobe 658-8558, Japan.
Brain Dev. 2015 Aug;37(7):669-76. doi: 10.1016/j.braindev.2014.10.006. Epub 2014 Oct 31.
More than 90% of spinal muscular atrophy (SMA) patients show homozygous deletion of SMN1 (survival motor neuron 1). They retain SMN2, a highly homologous gene to SMN1, which may partially compensate for deletion of SMN1. Although the promoter sequences of these two genes are almost identical, a GCC insertion polymorphism has been identified at c.-320_-321 in the SMN1 promoter. We have also found this insertion polymorphism in an SMN2 promoter in an SMA patient (Patient A) who has SMA type 2/3.
The aims of this study were to determine the frequency of the GCC insertion polymorphism in SMA patients, and to evaluate its effect on SMN transcription efficiency.
Fifty-one SMA patients, including Patient A, were involved in this study. SMN2 transcript levels in white blood cells were measured by real-time polymerase chain reaction. Screening of the GCC insertion polymorphism was performed using denaturing high-pressure liquid chromatography. The transcription efficiency of the promoter with the insertion mutation was evaluated using a reporter-gene assay.
All SMA patients in this study were homozygous for SMN1 deletion. Patient A retained two copies of SMN2, and showed only a small amount of SMN2 transcript in white blood cells. We detected a GCC insertion polymorphism at c.-320_-321 only in Patient A, and not in 50 other SMA patients. The polymorphism had a slight but significant negative effect on transcription efficiency.
Patient A was judged to be an exceptional case of SMA, because the GCC insertion polymorphism rarely exists in SMN1-deleted SMA patients. The GCC insertion polymorphism did not enhance the transcriptional efficiency of SMN2. Thus, this GCC insertion polymorphism in the SMN2 promoter may not be associated with the milder phenotype of the patient. Patient A suggests that there are other unknown factors modifying the clinical phenotype of SMA.
超过90%的脊髓性肌萎缩症（SMA）患者表现出SMN1（生存运动神经元1）的纯合缺失。他们保留了SMN2，这是一个与SMN1高度同源的基因，可能部分补偿SMN1的缺失。尽管这两个基因的启动子序列几乎相同，但在SMN1启动子的c.-320_-321处已鉴定出一个GCC插入多态性。我们还在一名患有2/3型SMA的SMA患者（患者A）的SMN2启动子中发现了这种插入多态性。
本研究的目的是确定SMA患者中GCC插入多态性的频率，并评估其对SMN转录效率的影响。
包括患者A在内的51名SMA患者参与了本研究。通过实时聚合酶链反应测量白细胞中的SMN2转录水平。使用变性高压液相色谱法进行GCC插入多态性的筛查。使用报告基因测定法评估具有插入突变的启动子的转录效率。
本研究中的所有SMA患者均为SMN1缺失的纯合子。患者A保留了两份SMN2，并且在白细胞中仅显示少量的SMN2转录本。我们仅在患者A中检测到c.-320_-321处的GCC插入多态性，而在其他50名SMA患者中未检测到。该多态性对转录效率有轻微但显著负面的影响。
患者A被判定为SMA的一个特殊病例，因为GCC插入多态性在缺失SMN1的SMA患者中很少存在。GCC插入多态性并未提高SMN2的转录效率。因此，SMN2启动子中的这种GCC插入多态性可能与患者较轻的表型无关。患者A表明存在其他未知因素改变SMA的临床表型。
