Chaturvedi L S, Mukherjee M, Srivastava S, Mittal R D, Mittal B
Department of Medical Genetics, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, India.
Exp Mol Med. 2001 Dec 31;33(4):251-6. doi: 10.1038/emm.2001.41.
Duchenne and Becker muscular dystrophies (D/BMD) are caused by mutations in the dystrophin gene. Two-thirds of patients have large intragenic deletions or duplications and the remaining one-third have point mutations, small deletions or insertions. Point mutations are more difficult to detect due to the enormous size (2.4 Mb) of the gene and its large transcript (14 kb). In the present study, a total of 50 DNA samples from unrelated D/BMD (38 DMD and 12 BMD) patients who did not show intragenic deletions by multiplex PCR, were analyzed for detection of point mutations. Single stranded conformation analysis and heteroduplex analysis observed electrophoretic mobility shifts in one (BMD) and two (DMD and BMD) patients, respectively. The mobility shift and heteroduplexes were observed in exon 17 in all of the three patients. Sequencing of the amplified PCR products revealed a nucleotide change (-37 g to t) in the intronic region in two of the patients while a C2268T substitution in the exonic region in one. Mutation database search for D/BMD mutations showed the nucleotide substitution in the exonic region as a novel change in the human dystrophin gene, which was not reported earlier. It resulted in an amino acid transition from threonine to methionine in the 687th position of the dystrophin protein. This novel substitution has been included in the mutation database of Leiden muscular dystrophy pages (http://www.dmd.nl) in the rare polymorphism/mutation category. The substituted nucleotide segregated with the disease phenotype in the family suggesting that it can be directly used for carrier detection and prenatal diagnosis without identification of disease causing mutation.
杜兴氏和贝克氏肌营养不良症（D/BMD）由肌营养不良蛋白基因突变引起。三分之二的患者存在大片段基因内缺失或重复，其余三分之一为点突变、小片段缺失或插入。由于该基因规模巨大（2.4 Mb）且转录本较长（14 kb），点突变更难检测。在本研究中，对50份来自无关D/BMD（38例DMD和12例BMD）患者的DNA样本进行分析，这些患者经多重PCR未显示基因内缺失，以检测点突变。单链构象分析和异源双链分析分别在1例（BMD）和2例（DMD和BMD）患者中观察到电泳迁移率变化。在所有3例患者的第17外显子中均观察到迁移率变化和异源双链。扩增的PCR产物测序显示，2例患者的内含子区域有核苷酸变化（-37 g突变为t），1例患者的外显子区域有C2268T替换。对D/BMD突变的数据库搜索显示，外显子区域的核苷酸替换是人类肌营养不良蛋白基因中的一种新变化，此前未见报道。它导致肌营养不良蛋白第687位氨基酸从苏氨酸转变为甲硫氨酸。这一新的替换已被列入莱顿肌营养不良症页面的突变数据库（http://www.dmd.nl）中的罕见多态性/突变类别。该替换核苷酸在家族中与疾病表型共分离，表明无需鉴定致病突变即可直接用于携带者检测和产前诊断。
