Genetics and Rare Diseases Research Division, Bambino Gesù Children's Hospital, IRCCS, 00146 Rome, Italy.
Department of Life, Health and Environmental Sciences University of L'Aquila, 00167 Rome, Italy.
Brain. 2021 Nov 29;144(10):3020-3035. doi: 10.1093/brain/awab185.
Leukodystrophies are a heterogeneous group of rare inherited disorders that mostly involve the white matter of the CNS. These conditions are characterized by primary glial cell and myelin sheath pathology of variable aetiology, which causes secondary axonal degeneration, generally emerging with disease progression. Whole exome sequencing performed in five large consanguineous nuclear families allowed us to identify homozygosity for two recurrent missense variants affecting highly conserved residues of RNF220 as the causative event underlying a novel form of leukodystrophy with ataxia and sensorineural deafness. We report these two homozygous missense variants (p.R363Q and p.R365Q) in the ubiquitin E3 ligase RNF220 as the underlying cause of this novel form of leukodystrophy with ataxia and sensorineural deafness that includes fibrotic cardiomyopathy and hepatopathy as associated features in seven consanguineous families. Mass spectrometry analysis identified lamin B1 as the RNF220 binding protein and co-immunoprecipitation experiments demonstrated reduced binding of both RNF220 mutants to lamin B1. We demonstrate that RNF220 silencing in Drosophila melanogaster specifically affects proper localization of lamin Dm0, the fly lamin B1 orthologue, promotes its aggregation and causes a neurodegenerative phenotype, strongly supporting the functional link between RNF220 and lamin B1. Finally, we demonstrate that RNF220 plays a crucial role in the maintenance of nuclear morphology; mutations in primary skin fibroblasts determine nuclear abnormalities such as blebs, herniations and invaginations, which are typically observed in cells of patients affected by laminopathies. Overall, our data identify RNF220 as a gene implicated in leukodystrophy with ataxia and sensorineural deafness and document a critical role of RNF220 in the regulation of nuclear lamina. Our findings provide further evidence on the direct link between nuclear lamina dysfunction and neurodegeneration.
脑白质营养不良是一组罕见的遗传性疾病，主要涉及中枢神经系统的白质。这些疾病的特征是原发性神经胶质细胞和髓鞘病理学的病因学变化，导致继发性轴突变性，通常随着疾病的进展而出现。在五个大型近亲核家族中进行的全外显子组测序使我们能够鉴定出两个反复出现的错义变异的纯合性，这些变异影响高度保守的 RNF220 残基，这是导致一种新型共济失调和感觉神经性耳聋脑白质营养不良的致病事件。我们报道了 RNF220 中的这两个纯合错义变异（p.R363Q 和 p.R365Q）是这种新型共济失调和感觉神经性耳聋脑白质营养不良的潜在原因，包括纤维性心肌病和肝病变作为七个近亲家族中相关特征。质谱分析鉴定了 lamin B1 作为 RNF220 的结合蛋白，共免疫沉淀实验证明了两种 RNF220 突变体与 lamin B1 的结合减少。我们证明了在果蝇中沉默 RNF220 会特异性影响 lamin Dm0（果蝇 lamin B1 的同源物）的正确定位，促进其聚集并导致神经退行性表型，这强烈支持了 RNF220 和 lamin B1 之间的功能联系。最后，我们证明了 RNF220 在维持核形态方面起着至关重要的作用；原发性皮肤成纤维细胞中的突变导致核异常，如泡状突起、疝出和内陷，这些异常通常在 laminopathies 患者的细胞中观察到。总之，我们的数据确定了 RNF220 是一种与共济失调和感觉神经性耳聋脑白质营养不良相关的基因，并证明了 RNF220 在核纤层调节中的关键作用。我们的研究结果为核纤层功能障碍与神经退行性变之间的直接联系提供了进一步的证据。
