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Updated: Dec 2, 2025

Targeted Next-generation Sequencing and Bioinformatics Pipeline to Evaluate Genetic Determinants of Constitutional Disease
Published on: April 4, 2018
POLR1C variants dysregulate splicing and cause hypomyelinating leukodystrophy
Hitoshi Kashiki1, Heng Li1, Sachiko Miyamoto1
1Department of Pediatrics (H.K.), Minamata City General Hospital & Medical Center, Kumamoto; Department of Mental Retardation and Birth Defect Research (H.L., K.I.), National Institute of Neuroscience, National Center of Neurology and Psychiatry, Kodaira, Tokyo; Department of Biochemistry (S.M., H.S.), Hamamatsu University School of Medicine, Shizuoka; Department of Pediatrics (H.U.), Kumamoto Takumadai Rehabilitation Hospital; Kanagawa Children's Medical Center (Y.T., Y.E.), Clinical Research Institute, Yokohama, Kanagawa; Department of Pediatrics (C.I., H.K., T.O., T.S., H.I.), National Hospital Organization Kumamoto Saishun Medical Center, Koshi; Clinical Research Institute, Kanagawa Children's Medical Center, (Y.E.), Yokohama, Kanagawa; Department of Pediatric Neurology (J.T.), Tokyo Women's Medical University Yachiyo Medical Center, Chiba; and Division of Medical Genetics (K.K.), Kanagawa Children's Medical Center, Yokohama, Japan.
Objective:
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.
Methods:
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.
Results:
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.
Conclusions:
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.
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