Mutations in valyl-tRNA synthetase gene VARS causing epleptic encephalopathy

Friedman J, Smith DE, Issa MY, Stanley V, Wang R, Mendes MI, Wright MS, Wigby K, Hildreth A, Crawford JR, Koehler AE, Chowdhury S, Nahas S, Zhai L, Xu Z, Lo WS, James KN, Musaev D, Accogli A, Guerrero K, Tran LT, Omar TEI, Ben-Omran T, Dimmock D, Kingsmore SF, Salomons GS, Zaki MS, Bernard G, Gleeson JG. Biallelic mutations in valyl-tRNA synthetase gene VARS are associated with a progressive neurodevelopmental epileptic encephalopathy. Nat Commun. 2019 Feb 12;10(1):707.

Abstract

Aminoacyl-tRNA synthetases (ARSs) function to transfer amino acids to cognate tRNA molecules, which are required for protein translation. To date, biallelic mutations in 31 ARS genes are known to cause recessive, early-onset severe multi-organ diseases. VARS encodes the only known valine cytoplasmic-localized aminoacyl-tRNA synthetase. Here, we report seven patients from five unrelated families with five different biallelic missense variants in VARS. Subjects present with a range of global developmental delay, epileptic encephalopathy and primary or progressive microcephaly. Longitudinal assessment demonstrates progressive cortical atrophy and white matter volume loss. Variants map to the VARS tRNA binding domain and adjacent to the anticodon domain, and disrupt highly conserved residues. Patient primary cells show intact VARS protein but reduced enzymatic activity, suggesting partial loss of function. The implication of VARS in pediatric neurodegeneration broadens the spectrum of human diseases due to mutations in tRNA synthetase genes.

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An international effort led by physician-scientists at Rady Children's Institute for Genomic Medicine (RCIGM), in collaboration with a team at the Montreal Children's Hospital of the McGill University Health Centre (MCH-MUHC), has identified the cause of a devastating pediatric brain disorder paving the way for the first step in developing potential therapies for this rare neurodegenerative condition.

Investigators performed advanced genetic tests on blood samples from seven children with neuro-development disabilities who were evaluated by doctors in San Diego, Montreal and Cairo. This led to the discovery of mutations in the VARS gene, which had not previously been linked to human disease.

"These children showed epileptic seizures and abnormalities evident on brain MRI scans," said Joseph Gleeson, MD, director of neurodevelopmental genetics at RCIGM and professor of neuroscience and pediatrics at UC San Diego School of Medicine. "Although no treatment currently exists for this condition, the results are important as the first step in guiding research directed at targeted therapies."

The genetic mutations identified in the study led to a defect in the enzyme responsible for generating proteins containing the amino acid valine which is necessary for cellular health. Genetic variations that damage these types of enzymes are associated with a variety of human diseases including microcephaly and neuropathy.

In this study, the team found that, enzymatic activity was significantly reduced in cells from the young patients. The findings suggest that children with this disorder may benefit from treatments to support the synthesis of new valine containing proteins in the brain…

Both whole exome and whole genome testing were conducted as part of this study. These tests search an individual's genetic code for imperfections that are the source of disease.

https://www.sciencedaily.com/releases/2019/02/190225100739.htm