中国人手足裂畸形患者中染色体10q24.3区域DNA重复突变的鉴定

A DNA duplication at chromosome 10q24.3 is associated with split-hand/split-foot malformation in a Chinese family

目的鉴定一个中国人手足裂畸形(SHFM)家系的致病突变,揭示该家系中手足裂畸形发生的分子遗传基础。方法回顾家系(4代共5例患者)中3例患者已有X线检查资料,补拍畸形手足外观照片。采集其中2例患者外周血进行高分辨G显带核型分析。从现有4名家系成员(包括3例患者)外周血样品中提取基因组DNA。针对TP63基因全部16个外显子(包括外显子/内含子交界区)设计并合成引物,以1例患者基因组DNA为模板进行聚合酶链反应(PCR)扩增和产物直接测序。在已知的5个SHFM位点染色体区域选择微卫星标记,通过PCR扩增和聚丙烯酰胺凝胶电泳分析家系成员的基因型。对染色体10q24.3区域SHFM3位点内微卫星标记的多态片段进行测序分析,比较患者和基因型相同的正常对照个体不同等位片段测序峰高度的差别。结果家系中现存3例患者双手均为桡侧指/掌骨缺失,2例患者双足表现中央轴趾/跖骨缺失,1例患者双足仅剩腓侧趾/跖骨,都符合典型手足裂畸形的临床表现。对患者进行高分辨G显带核型分析,未见染色体数目异常或结构畸变;对患者DNA进行TP63基因测序,未发现突变。通过检测微卫星标记进行基因型分析,发现患者在SHFM1、SHFM4和SHFM5三个位点不表现单体型共享,而在SHFM2和SHFM3两个位点则共享某一单体型,提示本家系中手足裂畸形表型可能由SHFM2或SHFM3位点的突变引起。进一步分析SHFM2和SHFM3两个位点微卫星标记的聚丙烯酰胺凝胶电泳结果,发现患者在SHFM3位点的患者共享等位片段呈现信号增强现象。以相同基因型正常人为对照个体进行微卫星标记的比较测序分析,发现患者间共享等位片段的测序峰在患者中增高约1倍。以上结果表明,本家系患者发生了SHFM3位点内的DNA重复。结论首次在中国人手足裂畸形患者中发现染色体10q24.3区域DNA重复突变。

Objective To identify the disease-causing genetic alteration of split-hand/split-foot malformation （SHFM） in a Chinese family. Methods Three of the 5 affected individuals from a fourgeneration Chinese SHFM family were examined physically and radiologically. Peripheral blood samples were collected from Digital photographs of the malformed hands and feet were taken. Peripheral blood samples were collected from 2 affected individuals, and lymphocytes were isolated to undergo high resolution Gbanding. Genomic DNA was extracted from the whole blood samples of 4 available family members, including the 3 affected individuals. All 16 exons and their flanking intronic sequences of the TP63 gene were amplified using polymerase chain reaction （PCR） and sequenced directly. Microsatellite markers from the five SHFM loci were analyzed in the available family members by PCR, polyacrylamide gel electrophoresis and silver staining. For semi-quantitative determination of the allele copy number, the polymorphic PCR-amplified fragments representing genetic markers from the SHFM3 locus at chromosome 10q24.3 were sequenced in the affected individuals using normal individuals with identical genotypes as controls. Results All 3 existing affected individuals showed absence of 3 radial fingers, 2 affected individuals had a deep central cleft and central ray deficiency in the feet, and 1 affected individual had a fibular monodactyly, all limb malformations being bilateral and consistent with the phenotype of typical SHFM. G-banding showed normal karyotypes in the 3 affected individuals and no visible cytogenetic abnormality was found. Moreover, no mutation was identified in the TP63 gene. While no haplotype sharing was observed in the markers from loci SHFM1, SHFM4 and SHFMS, potential haplotype sharing was detected in the markers from two loci, SHFM2 and SHFM3, indicating possible causative mutation at SHFM2 or SHFM3. Furthermore, obviously biased silver density toward the allele fragments shared by the 3 affected individuals was observed in the markers from the SHFM3 locus. Comparative sequencing showed roughly one-fold increase of fluorescent signal of the shared fragments in the affected individuals. These results suggested a large-scale DNA duplication within the SHFM3 locus. Conclusion A large-scale DNA duplication within the SHFM3 locus at chromosome 10q24. 3 has been identified as the pathogenic genetic change in Chinese patients with SHFM.