To further clarify the molecular pathogenesis of RNA polymerase III (Pol III)-related leukodystrophy caused by biallelic POLR1C variants at a cellular level and potential effects on its downstream genes.

Exome analysis and molecular functional studies using cell expression and long-read sequencing analyses were performed on 1 family with hypomyelinating leukodystrophy showing no clinical and MRI findings characteristic of Pol III–related leukodystrophy other than hypomyelination.

Biallelic novel POLR1C alterations, c.167T>A, p.M56K and c.595A>T, p.I199F, were identified as causal variants. Functional analyses showed that these variants not only resulted in altered protein subcellular localization and decreased protein expression but also caused abnormal inclusion of introns in 85% of the POLR1C transcripts in patient cells. Unexpectedly, allelic segregation analysis in each carrier parent revealed that each heterozygous variant also caused the inclusion of introns on both mutant and wild-type alleles. These findings suggest that the abnormal splicing is not direct consequences of the variants, but rather reflect the downstream effect of the variants in dysregulating splicing of POLR1C, and potentially other target genes.

The lack of characteristic clinical findings in this family confirmed the broad clinical spectrum of Pol III–related leukodystrophy. Molecular studies suggested that dysregulation of splicing is the potential downstream pathomechanism for POLR1C variants.

从细胞水平进一步阐明由双等位基因POLR1C变异引起的RNA聚合酶III（Pol III）相关脑白质营养不良的分子发病机制及其对下游基因的潜在影响。

使用细胞表达和长读长测序分析的外显子组分析和分子功能研究对 1 个患有低髓鞘质脑白质营养不良的家族进行，显示除髓鞘质减退外，没有 Pol III 相关脑白质营养不良的临床和 MRI 发现特征。

双等位基因新型POLR1C改变，c.167T>A，p.M56K 和 c.595A>T，p.I199F，被确定为因果变异。功能分析表明，这些变体不仅导致蛋白质亚细胞定位改变和蛋白质表达降低，而且还导致患者细胞中 85% 的POLR1C转录本异常包含内含子。出乎意料的是，每个携带者亲本的等位基因分离分析表明，每个杂合变体也导致突变和野生型等位基因上包含内含子。这些发现表明异常剪接不是变体的直接后果，而是反映了变体在调节POLR1C和潜在的其他靶基因的剪接中的下游效应。

该家族缺乏特征性临床发现证实了 Pol III 相关脑白质营养不良的广泛临床谱。分子研究表明，剪接失调是POLR1C变体的潜在下游病理机制。