Monoallelic POLR3A Variants Cause Early‐Onset Peripheral Neuropathy

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OBJECTIVE: Biallelic variants in genes encoding the RNA polymerase III complex (Pol III) cause a spectrum of neurological disorders primarily affecting the central nervous system. Monoallelic variants have been reported in the POLR3B subunit only, associated with neurodevelopmental disorder, epilepsy, and peripheral neuropathy. We describe a novel Pol III-related disorder caused by monoallelic variants in POLR3A and presenting primarily with peripheral neuropathy. METHODS: We performed clinical and genetic investigation of the affected families. Biophysical characterization of mutant proteins was performed in silico. Immunoblotting, interactomics, and transcriptomics characterization were done in cellular models. RESULTS: We identified 11 patients across 8 unrelated families harboring heterozygous missense variants in POLR3A, occurring de novo or segregating in an autosomal-dominant fashion. The patients presented with an early-onset, progressive sensorimotor peripheral polyneuropathy with intermediate to demyelinating ranges of nerve conduction slowing, occasionally accompanied with neurological or non-neurological features. White matter abnormalities, characteristic for the biallelic Pol III-related disorders, where not observed in the brain magnetic resonance imaging (MRI) evaluations. The neuropathy-associated variants cluster in regions critical for Pol III activity. We observed mis-regulation of individual Pol III targets and global downregulation of tRNA pools in patient-derived cells. This Pol III dysfunction was not due to impaired POLR3A expression, subcellular localization, or subunit interactions. INTERPRETATION: Our findings expand the Pol III-related disease spectrum beyond the known biallelic phenotypes and establish POLR3A as a novel peripheral neuropathy-associated gene. This work highlights a central role of Pol III dysfunction in disease and reinforces the link between tRNA metabolism and peripheral neurodegeneration. ANN NEUROL 2026;100:655-671.

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