A case of QARS1 associated epileptic encephalopathy and review of epilepsy in aminoacyl-tRNA synthetase disorders

Childhood-onset focal epilepsy and acute para-infectious encephalopathy in a patient with biallelic QARS1 variants

INTRODUCTION

Biallelic variants in QARS1, a house-keeping gene involved in protein synthesis, cause a rare encephalopathy classically characterized by severe developmental delay, drug-resistant neonatal-onset epilepsy, microcephaly, and brain atrophy. We aim to raise awareness on mild QARS1-related phenotypes describing a 6-year-old patient.

CASE DESCRIPTION

Epilepsy onset occurred at 3.5 years with a sleep-related focal autonomic seizure, accompanied by interictal occipital spikes at EEG. In the following months, daytime focal impaired awareness seizures appeared. Due to developmental delay and short stature, trio-based whole-exome sequencing was performed, unraveling two compound heterozygous QARS1 variants: the likely pathogenic c.1304A>G (p.Y435C) and the c.799C>T (p.R267W), extremely rare and predicted deleterious by in silico analysis. At 5 years, the patient had a para-infectious encephalopathy with acute psychomotor slowing, delta-theta activity at EEG, new-onset bilateral subcortical white matter T2-hyperintensities with diffusion restriction at brain MRI, and optimal response to intravenous methylprednisolone administration. At 12-month follow-up, the patient had been seizure-free for a year with levetiracetam monotherapy.

DISCUSSION

Mild QARS1-related encephalopathies may present with a childhood-onset focal epilepsy accompanied by developmental delay and short stature as red flags of monogenic etiology. The episode of steroid-responsive acute para-infectious encephalopathy, previously reported in another patient harboring the p.Y435C variant, suggests that milder cases might be more susceptible to encephalopathy caused by intercurrent illnesses (e.g., infection). As recommended for other aminoacyl-tRNA synthetase-related diseases, it is important to provide this cohort with an early genetic diagnosis in order to encourage precision medicine and personalized treatment.

Molecular analysis and prenatal diagnosis of seven Chinese families with genetic epilepsy

Introduction

Genetic epilepsy is a large group of clinically and genetically heterogeneous neurological disorders characterized by recurrent seizures, which have a clear association with genetic defects. In this study, we have recruited seven families from China with neurodevelopmental abnormalities in which epilepsy was a predominant manifestation, aiming to elucidate the underlying causes and make a precise diagnosis for the cases.

Methods

Whole-exome sequencing (WES) combined with Sanger sequencing was used to identify the causative variants associated with the diseases in addition to essential imaging and biomedical examination.

Results

A gross intragenic deletion detected in MFSD8 was investigated via gap-polymerase chain reaction (PCR), real-time quantitative PCR (qPCR), and mRNA sequence analysis. We identified 11 variants in seven genes (ALDH7A1, CDKL5, PCDH19, QARS1, POLG, GRIN2A, and MFSD8) responsible for genetic epilepsy in the seven families, respectively. A total of six variants (c.1408T>G in ALDH7A1, c.1994_1997del in CDKL5, c.794G>A in QARS1, c.2453C>T in GRIN2A, and c.217dup and c.863+995_998+1480del in MFSD8) have not yet been reported to be associated with diseases and were all evaluated to be pathogenic or likely pathogenic according to the American College of Medical Genetics and Genomics (ACMG) guidelines.

Methods

Based on the molecular findings, we have associated the intragenic deletion in MFSD8 with the mutagenesis mechanism of Alu-mediated genomic rearrangements for the first time and provided genetic counseling, medical suggestions, and prenatal diagnosis for the families. In conclusion, molecular diagnosis is crucial to obtain improved medical outcomes and recurrence risk evaluation for genetic epilepsy.

Aminoacyl-tRNA Synthetases: On Anti-Synthetase Syndrome and Beyond

Anti-synthetase syndrome (ASSD) is an autoimmune disease characterized by the presence of autoantibodies targeting one of several aminoacyl t-RNA synthetases (aaRSs) along with clinical features including interstitial lung disease, myositis, Raynaud’s phenomenon, arthritis, mechanic’s hands, and fever. The family of aaRSs consists of highly conserved cytoplasmic and mitochondrial enzymes, one for each amino acid, which are essential for the RNA translation machinery and protein synthesis. Along with their main functions, aaRSs are involved in the development of immune responses, regulation of transcription, and gene-specific silencing of translation. During the last decade, these proteins have been associated with cancer, neurological disorders, infectious responses, and autoimmune diseases including ASSD. To date, several aaRSs have been described to be possible autoantigens in different diseases. The most commonly described are histidyl (HisRS), threonyl (ThrRS), alanyl (AlaRS), glycyl (GlyRS), isoleucyl (IleRS), asparaginyl (AsnRS), phenylalanyl (PheRS), tyrosyl (TyrRS), lysyl (LysRS), glutaminyl (GlnRS), tryptophanyl (TrpRS), and seryl (SerRS) tRNA synthetases. Autoantibodies against the first eight autoantigens listed above have been associated with ASSD while the rest have been associated with other diseases. This review will address what is known about the function of the aaRSs with a focus on their autoantigenic properties. We will also describe the anti-aaRSs autoantibodies and their association to specific clinical manifestations, and discuss their potential contribution to the pathogenesis of ASSD.