在健康的个体中，凝血因子IX（固定）被合成为461个氨基酸前体（主要在肝脏）中，然后分泌到血浆中，在那里它将因子X转化为其活性形式。固定酶原经历了广泛的共同和翻译后修饰，包括但不限于糖基化和γ-羧化。由F9基因突变引起的固定缺乏或功能障碍与血液凝血嗜血症B（HB）相关。通过影响固定蛋白质合成，稳定性或分泌物的F9突变在循环中可以降低固定蛋白质水平。Fix的羧基末端区域含有几种天然畸形突变，例如Y450C，W453R和T458K，其损害了修复的分泌并导致MILD至严重形式的HB（Kurachi S等人1997; Branchini A等，2013）。此外，F9基因的外显子5包含与氨基酸代码重叠的密集剪接调节信息（Tajnik M等人2016）。在正常条件下，外显子5被缩写物组正确识别，并且大多包括在最终的转录物中。这导致生产正常固定蛋白，其在内质网（ER）中正确折叠，并有效地分泌到血液中以激活凝结。在外显子5中的结果外显子跳跃数F9突变（Tajnik M等人2016; Odaira K等人2019; Katneni UK等人2019）。外源剪接突变（ESM）可分为三个主要组，其定义其分子基础。 In the first group, two synonymous variants, V153V and R162R, affect binding of splicing factors and induce severe exon skipping with the production of a non-functional mRNA (Tajnik M et al. 2016). The second type of ESM, such as A164V and Q167H, showed partial splicing defects producing low amounts of normally spliced transcript that, when translated, resulted in a defective FIX protein with a significantly reduced, but not completely abolished, secretion. However, the lower amounts of the secreted proteins maintained a normal specific coagulant activity. Lastly, mutation L163F (ESM group 3) showed a splicing defect but the resulting amino acid change severely affected FIX secretion (Tajnik M et al. 2016). Another HB-associated F9 variant caused abnormal mRNA splicing, r.83_88del, and produced the mutant FIX protein (p.C28_V30delinsF), which is an in-frame mutant at the signal peptide cleavage site (Odaira K et al. 2019). The FIX C28_V30delinsF variant was found to be retained in the ER without being secreted (Odaira K et al. 2019). Studies also showed defective secretion of HB-associated F9 nonsense mutations such as R294*, R298* and R384* (Branchini A et al. 2017; Pinotti M et al. 2012). The mechanism through which nonsense mutations impair gene expression and cause human genetic disease consists of premature translation termination, and the synthesis of truncated proteins with loss‐of‐function features (Mort M et al. 2008). These mutations can trigger nonsense‐mediated decay of mRNA, that degrades mRNA transcripts that harbor a premature translation-termination codon (PTC), thus reducing the synthesis of truncated proteins (Khajavi et al. 2006; Kurosaki T & Maquat LE 2016). However, the mechanism of ribosome readthrough, which consists of misrecognition of the premature stop codon by an aminoacyl‐tRNA instead of the termination factors can restore translation impaired by nonsense mutations (Rospert S et al. 2005). The occurrence of spontaneous ribosome readthrough over F9 R294* and F9 R298* nonsense mutations led to the synthesis of traces of full‐length FIX in HB patients (Pinotti M et al. 2012). A drug-induced ribosome readthrough targeting nonsense variants is considered as a potential treatment of inherited coagulation factor disorders (Branchini A et al. 2017; Ferrarese M et al. 2018; Balestra D & Branchini A 2019).

由于在整个F9基因中扩散的不同HB相关的遗传改变，反应性事件描述了细胞内积聚和/或减少的修复分泌。关于蛋白质序列的变化描述F9变体。这里没有显示F9突变诱导的剪接事件。