Aims Rare, deleterious genetic variants in FLT4 are associated with Tetralogy of Fallot (TOF), the most common cyanotic congenital heart disease (CHD). Distinct genetic variants in FLT4 are also an established cause of Milroy disease, the most prevalent form of primary hereditary lymphoedema. Phenotypic features of these two conditions are non-overlapping, implying pleiotropic cellular mechanisms during development. Methods and Results Here, we show that FLT4 variants identified in TOF patients, when expressed in primary human endothelial cells, cause aggregation of FLT4 protein in the perinuclear endoplasmic reticulum, activating proteostatic and metabolic signalling, whereas lymphoedema-associated FLT4 variants and wildtype FLT4 do not. FLT4 TOF variants display characteristic gene expression profiles in key developmental signalling pathways, revealing a role for FLT4 in cardiogenesis distinct from its role in lymphatic development. Inhibition of proteostatic signalling abrogates these effects, identifying potential avenues for therapeutic intervention. Depletion of flt4 in zebrafish caused cardiac phenotypes of reduced heart size and altered heart looping. These phenotypes were rescued with coinjection of wildtype human FLT4 mRNA, but incompletely or not at all by mRNA harbouring FLT4 TOF variants. Conclusions Taken together, we identify a pathogenic mechanism for FLT4 variants predisposing to TOF that is distinct from the known dominant negative mechanism of Milroy-causative variants. FLT4 variants give rise to conditions of the two circulatory subdivisions of the vascular system via distinct developmental pleiotropic molecular mechanisms. Translational Perspective Proteostatic dysfunction, if confirmed as a mechanism of CHD pathogenesis for other predisposing genes, may identify pathways to therapeutic interventions. Distinguishing mechanistically how variants in FLT4 give rise to CHD may have potential to individualise genetic counselling in affected families.

中文翻译：

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FLT4通过多效性分子机制引起心血管和淋巴血管系统的发育障碍

FLT4 中罕见的有害遗传变异与法洛四联症 (TOF) 相关，这是最常见的紫绀型先天性心脏病 (CHD)。 FLT4 的独特遗传变异也是 Milroy 病（原发性遗传性淋巴水肿最常见的形式）的一个确定原因。这两种条件的表型特征不重叠，暗示发育过程中的多效性细胞机制。方法和结果在此，我们表明，在 TOF 患者中鉴定的 FLT4 变异体，当在原代人内皮细胞中表达时，会导致 FLT4 蛋白在核周内质网中聚集，激活蛋白抑制和代谢信号传导，而淋巴水肿相关的 FLT4 变异体和野生型 FLT4 则不会发生这种情况。不是。 FLT4 TOF 变体在关键发育信号通路中显示出特征性基因表达谱，揭示了 FLT4 在心脏发生中的作用与其在淋巴管发育中的作用不同。抑制蛋白质信号传导可以消除这些影响，从而确定治疗干预的潜在途径。斑马鱼中 flt4 的缺失会导致心脏尺寸减小和心脏循环改变的心脏表型。这些表型通过共注射野生型人FLT4 mRNA得到挽救，但通过含有FLT4 TOF变体的mRNA不完全或根本没有挽救。结论 综上所述，我们确定了导致 TOF 的 FLT4 变异的致病机制，该机制与 Milroy 致病变异已知的显性失活机制不同。 FLT4变体通过不同的发育多效性分子机制引起血管系统两个循环细分的状况。转化视角如果蛋白质稳态功能障碍被证实是其他诱发基因的冠心病发病机制，则可能会确定治疗干预的途径。从机制上区分 FLT4 变异如何导致冠心病可能有可能为受影响的家庭提供个体化的遗传咨询。