A new entity in the NARS2 variant: the first reported case of type 1 diabetes mellitus associated with the phenotype

Novel NARS2 variants in a patient with early-onset status epilepticus: case study and literature review

BACKGROUND

NARS2 as a member of aminoacyl-tRNA synthetases was necessary to covalently join a specific tRNA to its cognate amino acid. Biallelic variants in NARS2 were reported with disorders such as Leigh syndrome, deafness, epilepsy, and severe myopathy.

CASE PRESENTATION

Detailed clinical phenotypes were collected and the NARS2 variants were discovered by whole exome sequencing and verified by Sanger sequencing. Additionally, 3D protein structure visualization was performed by UCSF Chimera. The proband in our study had early-onset status epilepticus with abnormal EEG and MRI results. She also performed global developmental delay (GDD) and myocardial dysfunction. Next-generation sequencing (NGS) and Sanger sequencing revealed compound heterozygous missense variants [NM_024678.6:exon14: c.1352G > A(p.Arg451His); c.707T > C(p.Phe236Ser)] of the NARS2 gene. The proband develops refractory epilepsy with GDD and hyperlactatemia. Unfortunately, she finally died for status seizures two months later.

CONCLUSION

We discovered two novel missense variants of NARS2 in a patient with early-onset status epilepticus and myocardial dysfunction. The NGS enables the patient to be clearly diagnosed as combined oxidative phosphorylation deficiency 24 (COXPD24, OMIM:616,239), and our findings expands the spectrum of gene variants in COXPD24.

Progressive Mitochondrial Encephalopathy Due to the Novel Compound Heterozygous Variants c.182C>T and c.446A>AG in NARS2: A Case Report

Progressive mitochondrial encephalopathy manifesting as developmental delay, regression, epilepsy, myoclonus, dystonia, and spasticity due to a novel compound heterozygous variant in NARS2 has not been reported. The patient is a 3.5-year-old female with normal psychomotor development until she experienced her first generalized status epilepticus at 4.5 months of age. After seizure control, generalized myoclonus and psychomotor regression became evident. She suffered from two other epileptic states and seizure control remained inadequate despite the use of multiple anti-seizure drugs. Neurologic examination revealed generalized hypotonia, discoordination, unstable eye contact, drooling, open mouth, myoclonus, periodic torticollis, and ankle contractions. Cerebral MRI revealed hydrocephalus ex vacuo due to diffuse cortical and subcortical atrophy bilaterally and incomplete myelination. Genetic testing at 12 months of age revealed the compound heterozygous variants chr11: 78204182C>T and chr11: 78282446A>AG in NARS2. Despite anti-seizure drugs, mitochondrial cocktail, and cannabidiol, the disease progressed to intractable seizures and severe tetraspasticity. In summary, this case demonstrates that compound heterozygous variants in NARS2 can phenotypically manifest exclusively in the brain with intractable epilepsy, myoclonus, developmental delay, regression, hypotonia, cerebral atrophy, and hypomyelination, followed by tetraspasticity and dystonia.