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Abstract：
Marfan syndrome (MFS) is an autosomal dominant connective tissue disorder that canonically affects the ocular, skeletal, and cardiovascular system, in which aortic tear and rupture is the leading cause of death for MFS patients. Genetically, MFS is primarily associated with fibrillin-1 (FBN1) pathogenic variants. However, the disease-causing variant in approximately 10% of patients cannot be identified, partly due to some cryptic mutations that may be missed using routine exonic sequencing, such as non-coding intronic variants that affects the RNA splicing process. We present a 32-year female with typical MFS systemic presentation that reached to a clinical diagnosis according to the revised Ghent nosology. We performed whole-exome sequencing (WES) but the report failed to identify known causal variants when analyzing the exonic sequence. However, further investigation on the exon/intron boundaries of the WES report revealed a candidate intronic variant of the fibrillin 1 (FBN1) gene (c.248-3 C>G) that predicted to affect the RNA splicing process. We conducted minigene splicing analyses and demonstrated that the c.248-3 C>G variant abolished the canonical splicing site of intron 3, leading to activation of two cryptic splicing sites and causing insertion (c.248-1_248-2insAG and c.248-1_248-282ins). Our study not only characterizes an intronic variant to the mutational spectrum of the FBN1 gene in MFS and its aberrant effect on splicing, but highlights the importance to not neglect the exon/intron boundaries when reporting and assessing WES results. We point out the need of conducting functional analysis to verify the pathogenicity of intronic mutation, and the opportunity to re-consider the standard diagnostic approaches in cases of clinically diagnosed MFS with normal or variant of unknown significance genetic results.
摘要：
马凡氏综合征（MFS）是一种常染色体显性遗传性结缔组织疾病，主要影响眼部，骨骼，和心血管系统，其中主动脉撕裂和破裂是MFS患者死亡的主要原因。基因上,MFS主要与纤丝蛋白-1(FBN1)致病变体相关。然而,大约10%的患者的致病变异无法识别，部分原因是一些使用常规外显子测序可能会错过的隐性突变，例如影响RNA剪接过程的非编码内含子变体。我们介绍了一名32岁的女性，其典型的MFS系统表现根据修订的根特疾病学进行临床诊断。我们进行了全外显子组测序（WES），但该报告在分析外显子序列时未能确定已知的因果变异。然而,对WES报告的外显子/内含子边界的进一步研究揭示了原纤维蛋白1(FBN1)基因的候选内含子变体(c.248-3C>G),其预测会影响RNA剪接过程.我们进行了小基因剪接分析，并证明c.248-3C>G变体消除了内含子3的经典剪接位点，导致两个隐蔽剪接位点的激活并导致插入（c.248-1_248-2insAG和c.248-1_248-282ins）。我们的研究不仅描述了MFS中FBN1基因突变谱的内含子变体及其对剪接的异常影响，但强调了在报告和评估WES结果时不要忽视外显子/内含子界限的重要性.我们指出需要进行功能分析来验证内含子突变的致病性，以及在临床诊断为MFS且遗传结果正常或变异未知的情况下重新考虑标准诊断方法的机会。
