De novo POLR2A p.(Ile457Thr) variant associated with early-onset encephalopathy and cerebellar atrophy: expanding the phenotypic spectrum

Abstract

Background: Heterozygous POLR2A variants have been recently reported in patients with a neurodevelopmental syndrome characterized by profound infantile-onset hypotonia. POLR2A encodes the highly conserved RBP1 protein, an essential subunit of the DNA-dependent RNA polymerase II.

Case presentation: We investigated a 12-year-old girl presenting with an early-onset encephalopathy characterized by psychomotor delay, facial dysmorphism, refractory epilepsy with variable seizure types, behavioural abnormalities, and sleep disorder. Brain MRI showed a slowly progressive cerebellar atrophy. Trio-exome sequencing (Trio-ES) revealed the de novo germline variant NM_000937.5:c.1370T>C; p.(Ile457Thr) in POLR2A. This variant was previously reported in a subject with profound generalized hypotonia and muscular atrophy by Haijes et al. Our patient displayed instead a severe epileptic phenotype with refractory hypotonic seizures with impaired consciousness, myoclonic jerks, and drop attacks.

Conclusion: This case expands the clinical spectrum of POLR2A-related syndrome, highlighting its phenotypic variability and supporting the relevance of epilepsy as a core feature of this emerging condition.

Keywords: Cerebellar atrophy; Epileptic encephalopathy; Neurodevelopmental disorder; POLR2A; Sleep disorder.