Novel RARS2 Variants: Updating the Diagnosis and Pathogenesis of Pontocerebellar Hypoplasia Type 6

Yi Zhang; Yafen Yu; Xiangyue Zhao; Yufei Xu; Lina Chen; Niu Li; Ruen Yao; Jian Wang; Tingting Yu

doi:10.1016/j.pediatrneurol.2022.04.002

Novel RARS2 Variants: Updating the Diagnosis and Pathogenesis of Pontocerebellar Hypoplasia Type 6

Pediatr Neurol. 2022 Jun:131:30-41. doi: 10.1016/j.pediatrneurol.2022.04.002. Epub 2022 Apr 15.

Authors

Yi Zhang¹, Yafen Yu², Xiangyue Zhao¹, Yufei Xu¹, Lina Chen¹, Niu Li¹, Ruen Yao¹, Jian Wang³, Tingting Yu⁴

Affiliations

¹ Department of Medical Genetics and Molecular Diagnostic Laboratory, Shanghai Children's Medical Center, School of Medicine, Shanghai Jiao Tong University, Shanghai, People's Republic of China.
² Department of Children's Health Prevention, Tianshui First People's Hospital, Gansu, People's Republic of China.
³ Department of Medical Genetics and Molecular Diagnostic Laboratory, Shanghai Children's Medical Center, School of Medicine, Shanghai Jiao Tong University, Shanghai, People's Republic of China. Electronic address: labwangjian@shsmu.edu.cn.
⁴ Department of Medical Genetics and Molecular Diagnostic Laboratory, Shanghai Children's Medical Center, School of Medicine, Shanghai Jiao Tong University, Shanghai, People's Republic of China. Electronic address: yutingting@scmc.com.cn.

PMID: 35468344
DOI: 10.1016/j.pediatrneurol.2022.04.002

Abstract

Background: Pontocerebellar hypoplasia type 6 (PCH6) is an early-onset encephalopathy with/without mitochondrial respiratory complex defects caused by recessive mutations in mitochondrial arginyl-tRNA synthetase (RARS2). Highly heterogeneous clinical phenotypes and numerous missense variations of uncertain significance make diagnosis difficult. Pathogenesis of PCH6 remains unclear.

Methods: Facial characteristics of patients were assessed. Genetic tests were performed. Structure prediction was based on the template from AlphaFold Protein Structure Database. Expression of mutant RARS2 was tested in HEK293T cells. Patient-derived induced pluripotent stem cells (iPSCs) were detected for human mitochondrial tRNA^Arg (hmtRNA^Arg) steady-state level, mitochondrial respiratory complex (MRC) activity, oxygen consumption rate (OCR), extracellular acidification rate (ECAR), mitochondrial membrane potential (MMP), reactive oxygen species (ROS) abundance, and apoptosis level.

Results: The three pedigrees were diagnosed as PCH6 caused by compound heterozygous RARS2 variations. Five RARS2 variants were identified: c.3G>C(p.M1?), c.685C>T(p.R229∗), c.1060T>A(p.F354I), c.1210A>G(p.M404V), and c.1369G>A(p.G457R). RARS2 c.3G>C disrupted protein expression. RARS2 c.685C>T created a truncated protein lacking complete catalytic core and anticodon-binding domain. RARS2 c.1060T>A and c.1369G>A were predicted to cause structural abnormality. The hmtRNA^Arg steady-state abundance in a patient's iPSCs was unaffected. Mitochondrial energy metabolism was normal, including MRC activity, OCR, ECAR, and MMP, while mitochondria-related cellular characteristics, including ROS (P < 0.001) and apoptosis levels (P < 0.001), increased.

Conclusions: This study reports five RARS2 variations among which c.3G>C and c.1060T>A are novel. Summarized facial features of PCH6 patients will facilitate diagnosis. Defective mitochondrial energy metabolism may not be key points, but mitochondria-related abnormal cellular physiology, including apoptosis, may be an underlying pathogenesis.

Keywords: Apoptosis; Facial feature; Mitochondria; Pontocerebellar hypoplasia type 6; RARS2.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Arginine-tRNA Ligase* / genetics
HEK293 Cells
Humans
Mutation / genetics
Olivopontocerebellar Atrophies* / diagnosis
Olivopontocerebellar Atrophies* / pathology
Reactive Oxygen Species

Substances

Arginine-tRNA Ligase
RARS2 protein, human
Reactive Oxygen Species

Supplementary concepts

Pontocerebellar Hypoplasia Type 6