Document Type

Article

Publication Date

10-13-2023

Identifier

DOI: 10.3389/fneur.2023.1254140; PMCID: PMC10616956

Abstract

RNA polymerase III-related leukodystrophy (POLR3-related leukodystrophy) is a rare, genetically determined hypomyelinating disease arising from biallelic pathogenic variants in genes encoding subunits of RNA polymerase III (Pol III). Here, we describe the first reported case of POLR3-related leukodystrophy caused by biallelic pathogenic variants in POLR3D, encoding the RPC4 subunit of Pol III. The individual, a female, demonstrated delays in walking and expressive and receptive language as a child and later cognitively plateaued. Additional neurological features included cerebellar signs (e.g., dysarthria, ataxia, and intention tremor) and dysphagia, while non-neurological features included hypodontia, hypogonadotropic hypogonadism, and dysmorphic facial features. Her MRI was notable for diffuse hypomyelination with myelin preservation of early myelinating structures, characteristic of POLR3-related leukodystrophy. Exome sequencing revealed the biallelic variants in POLR3D, a missense variant (c.541C > T, p.P181S) and an intronic splice site variant (c.656-6G > A, p.?). Functional studies of the patient's fibroblasts demonstrated significantly decreased RNA-level expression of POLR3D, along with reduced expression of other Pol III subunit genes. Notably, Pol III transcription was also shown to be aberrant, with a significant decrease in 7SK RNA and several distinct tRNA genes analyzed. Affinity purification coupled to mass spectrometry of the POLR3D p.P181S variant showed normal assembly of Pol III subunits yet altered interaction of Pol III with the PAQosome chaperone complex, indicating the missense variant is likely to alter complex maturation. This work identifies biallelic pathogenic variants in POLR3D as a novel genetic cause of POLR3-related leukodystrophy, expanding the molecular spectrum associated with this disease, and proposes altered tRNA homeostasis as a factor in the underlying biology of this hypomyelinating disorder.

Journal Title

Front Neurol

Volume

14

First Page

1254140

Last Page

1254140

Keywords

4H leukodystrophy; POLR3-related leukodystrophy; POLR3D; RNA polymerase III; RPC4; hypomyelination

Comments

Grants and funding

This work was supported by project grants from the Canadian Institutes of Health Research (377869, 426534) as well as research grants from the Montreal Children’s Hospital Foundation and Leuco-Action. GB has received the Clinical Research Scholar Junior 1 Award from the Fonds de Recherche du Quebec-Santé (FRQS; 2012–2016), the New Investigator Salary Award from the Canadian Institutes of Health Research (2017–2022), and the Clinical Research Scholar Senior Award from the FRQS (2022–2025). This research was undertaken thanks in part to funding from the Canada First Research Excellence Fund and Fonds de recherche du Québec, awarded to the Healthy Brain Healthy Lives (HBHL) initiative at McGill University. JM is supported by HBHL. SP has been supported by the FRQS Doctoral Scholarship, the Fondation du Grand Défi Pierre Lavoie Doctoral Scholarship, the McGill Faculty of Medicine F.S.B. Miller Fellowship, and the Research Institute of the McGill University Health Center Desjardins Studentship in Child Health Research. The work by TP and IT was made possible by the generous gifts to Children’s Mercy Research Institute and Genomic Answers for Kids program at Children’s Mercy Kansas City. TP holds the Dee Lyons/Missouri Endowed Chair in Pediatric Genomic Medicine.

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

Publisher's Link: https://www.frontiersin.org/articles/10.3389/fneur.2023.1254140/full

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