Department of Internal Medicine, University of Texas Health Science Center at Houston (UTHealth), Houston, Texas, USA.
Department of Internal Medicine, WVU School of Medicine-Charleston Division (Retired), Morgantown, West Virginia, USA.
Clin Genet. 2023 Jun;103(6):704-708. doi: 10.1111/cge.14322. Epub 2023 Mar 7.
Exome sequencing of genes associated with heritable thoracic aortic disease (HTAD) failed to identify a pathogenic variant in a large family with Marfan syndrome (MFS). A genome-wide linkage analysis for thoracic aortic disease identified a peak at 15q21.1, and genome sequencing identified a novel deep intronic FBN1 variant that segregated with thoracic aortic disease in the family (LOD score 2.7) and was predicted to alter splicing. RT-PCR and bulk RNA sequencing of RNA harvested from fibroblasts explanted from the affected proband revealed an insertion of a pseudoexon between exons 13 and 14 of the FBN1 transcript, predicted to lead to nonsense mediated decay (NMD). Treating the fibroblasts with an NMD inhibitor, cycloheximide, greatly improved the detection of the pseudoexon-containing transcript. Family members with the FBN1 variant had later onset aortic events and fewer MFS systemic features than typical for individuals with haploinsufficiency of FBN1. Variable penetrance of the phenotype and negative genetic testing in MFS families should raise the possibility of deep intronic FBN1 variants and the need for additional molecular studies.
对与遗传性胸主动脉疾病 (HTAD) 相关的基因进行外显子组测序未能在一个患有马凡综合征 (MFS) 的大型家族中发现致病性变异。对胸主动脉疾病的全基因组连锁分析在 15q21.1 处发现了一个峰值，基因组测序发现了一种新型的 FBN1 基因深内含子变异，该变异与家族中的胸主动脉疾病分离 (LOD 评分 2.7)，并预测会改变剪接。从受影响的先证者的成纤维细胞中提取的 RNA 进行 RT-PCR 和批量 RNA 测序，揭示了 FBN1 转录本的 13 号和 14 号外显子之间插入了一个假外显子，预测会导致无意义介导的衰变 (NMD)。用 NMD 抑制剂环己酰亚胺处理成纤维细胞，大大提高了含有假外显子的转录本的检测。携带 FBN1 变异的家族成员的主动脉事件发生较晚，且 MFS 系统特征比 FBN1 单倍不足的个体典型特征更少。表型的可变外显率和 MFS 家族中的阴性遗传检测应提示存在 FBN1 基因深内含子变异的可能性，并需要进行额外的分子研究。
