迟发性脊柱骨骺发育不良家系基因诊断及遗传学发病机制分析

Genetic diagnosis and analysis of the pathogenic mechanism for spondyloepiphyseal dysplasia tarda in a Chinese family

目的迟发性脊柱骨骺发育不良(spondyloepiphyseal dysplasia tarda,SEDT)是一种X-连锁隐性遗传的骨软骨发育不良疾病,主要特征包括非匀称性短躯干型身材矮小及特征性的X线片表现。目前,导致该病的已知致病基因为SEDL基因。该文的主要目的是对一个来自湖南的SEDT家系进行基因诊断和遗传学发病机制分析。方法对一例迟发性非匀称性短躯干型身材矮小的患者进行家系分析和临床诊断;采集患者及其母亲外周血,进行DNA抽提后,对SEDL基因4个外显子的编码区进行PCR扩增;琼脂糖凝胶电泳分析PCR产物是否存在及其大小;对未成功扩增的外显子进行长PCR扩增,并对长PCR扩增得到的截短PCR产物进行测序分析。结果患者存在一个大小为1 327 bp的缺失,该缺失包括部分第5内含子和第6外显子编码区;患者母亲为该缺失的携带者。对缺失序列及其侧翼序列进行分析,发现第5内含子存在一个Alu序列,与第6外显子非编码区4个Alu序列序列高度相似;提示这些Alu序列的存在可能是SEDL基因发生类似缺失突变的遗传性发病机制的分子结构基础。结论该文在一个湖南家系中发现的SEDL基因缺失突变,即包括第6外显子编码区在内的1 327 bp缺失,是一个新发现的国际上尚未报道的突变。对SEDL基因的突变检测有助于患者迟发性脊柱骨骺发育不良的确诊,也为女性携带者的诊断,产前诊断和遗传咨询奠定重要的前提基础。

[ Objective ] Spondyloepiphyseal dysplasia tarda （SEDT） is an X-linked recessive osteochondrodysplasia characterized by disproportionate short stature with short trunk and distinctive radiological signs. SEDL gene is known to be responsible for SEDT. The purpose of this study is to identify the genetic defect of SEDT in a family from Hunan province and elucidate its possible genetic pathogenic mechanism. [Methods ] Clinical examinations on a patient presenting with disproportionate short stature with short trunk and pedigree analysis was performed. Genomic DNA was extracted from the peripheral blood leucocytes from the proband and his mother under informed consent. The four coding exons of the SEDL gene were amplified by polymerase chain reaction （PCR）. Agarose gel electrophoresis was performed to determine the presence and size of the PCR products. The failed PCR amplification was further Validated by long range PCR. The shortened PCR fragments generated in long range PCR were directly sequenced. [Results] A deletion of 1 327 bp encompassing partial intron 5 and the coding region of exon 6 in the SEDL gene was identified in the proband. His unaffected mother was the carrier of this deletion. Genetic information analysis of the sequences of the deletion and its flanking regions revealed that an Alu sequence in the intron 5 has a high similarity with four Alu sequences located in the un-coding region of exon 6 in the SEDL gene. These Alu sequences could facilitate the elucidation of the genetic pathogenic mechanism for the SEDT caused by similar deletions. [ Conclusion ] We found a novel deletion of 1 327 bp containing the coding region of exon 6 in the SEDL gene in a family from Hunan province. Mutation screening of the SEDL gene would facilitate the genetic diagnosis of the SEDT in the patients and it provides an important prerequisite for female cartier detection and prenatal diagnosis, and the genetic counseling.