RESUMEN
Progressive microcephaly and neurodegeneration are genetically heterogenous conditions, largely associated with genes that are essential for the survival of neurons. In this study, we interrogate the genetic etiology of two siblings from a non-consanguineous family with severe early onset of neurological manifestations. Whole exome sequencing identified novel compound heterozygous mutations in VARS that segregated with the proband: a missense (c.3192G>A; p.Met1064Ile) and a splice site mutation (c.1577-2A>G). The VARS gene encodes cytoplasmic valyl-tRNA synthetase (ValRS), an enzyme that is essential during eukaryotic translation. cDNA analysis on patient derived fibroblasts revealed that the splice site acceptor variant allele led to nonsense mediated decay, thus resulting in a null allele. Three-dimensional modeling of ValRS predicts that the missense mutation lies in a highly conserved region and could alter side chain packing, thus affecting tRNA binding or destabilizing the interface between the catalytic and tRNA binding domains. Further quantitation of the expression of VARS showed remarkably reduced levels of mRNA and protein in skin derived fibroblasts. Aminoacylation experiments on patient derived cells showed markedly reduced enzyme activity of ValRS suggesting the mutations to be loss of function. Bi-allelic mutations in cytoplasmic amino acyl tRNA synthetases are well-known for their role in neurodegenerative disorders, yet human disorders associated with VARS mutations have not yet been clinically well characterized. Our study describes the phenotype associated with recessive VARS mutations and further functional delineation of the pathogenicity of novel variants identified, which widens the clinical and genetic spectrum of patients with progressive microcephaly.
Asunto(s)
Atrofia/genética , Microcefalia/genética , Convulsiones/genética , Valina-ARNt Ligasa/genética , Alelos , Aminoacil-ARNt Sintetasas/genética , Atrofia/fisiopatología , Preescolar , Regulación Enzimológica de la Expresión Génica , Humanos , Lactante , Mutación con Pérdida de Función/genética , Masculino , Microcefalia/fisiopatología , Linaje , ARN de Transferencia/genética , Proteínas de Unión al ARN/genética , Convulsiones/fisiopatología , Aminoacilación de ARN de Transferencia/genética , Secuenciación del ExomaRESUMEN
We here establish a mouse cancer model called Multi-Hit that allows for the evaluation of oncogene cooperativities in tumor development. The model is based on the stochastic expression of oncogene combinations ('hits') that are mediated by Cre in a given tissue. Cells with cooperating hits are positively selected and give rise to tumors. We used this approach to evaluate the requirement of Ras downstream effector pathways in tumorigenesis.
