title: The pathogenicity scoring system for mitochondrial tRNA mutations revisited.
abstract: Confirming the pathogenicity of mitochondrial tRNA point mutations is one of the classical challenges in the field of mitochondrial medicine. In addition to genetic and functional studies, the evaluation of a genetic change using a pathogenicity scoring system is extremely useful to discriminate between disease-causing mutations from neutral polymorphisms. The pathogenicity scoring system is very robust for confirming pathogenicity, especially of mutations that show impaired activity in functional studies. However, mutations giving normal results using the same functional approaches are disregarded, and this compromises the power of the system to rule out pathogenicity. We propose to include a new criterion in the pathogenicity scoring systems regarding mutations which fail to show any mitochondrial defect in functional studies. To evaluate this proposal we characterized two mutations, m.8296A>G and m.8347A>G, in the mitochondrial tRNA(L) (ys) gene (MT-TK) using trans-mitochondrial cybrid analysis. m.8347A>G mutation severely impairs oxidative phosphorylation, suggesting that it is highly pathogenic. By contrast, the behavior of cybrids homoplasmic for the m.8296A>G mutation is similar to cybrids containing wild-type mitochondrial DNA (mtDNA). The results indicate that including not only positive but also negative outcomes of functional studies in the scoring system is critical for facilitating the diagnosis of this complex group of diseases.
authors.affiliation: Departamento de Bioquímica, Instituto de Investigaciones Biomédicas "Alberto Sols" UAM-CSIC and Centro de Investigación Biomédica en Red de Enfermedades Raras (CIBERER), Universidad Autónoma de Madrid 28029, Madrid, Spain ; Laboratorio de Enfermedades Mitocondriales, Instituto de Investigación Sanitaria Hospital 12 de Octubre (i+12) Madrid, Spain.
authors.forename: Emiliano
authors.initials: E
authors.lastname: González-Vioque
authors.affiliation: Departamento de Bioquímica, Instituto de Investigaciones Biomédicas "Alberto Sols" UAM-CSIC and Centro de Investigación Biomédica en Red de Enfermedades Raras (CIBERER), Universidad Autónoma de Madrid 28029, Madrid, Spain ; Servicio de Bioquímica, Instituto de Investigación Sanitaria Puerta de Hierro Majadahonda Madrid, Spain.
authors.forename: Belén
authors.initials: B
authors.lastname: Bornstein
authors.affiliation: Departamento de Bioquímica, Instituto de Investigaciones Biomédicas "Alberto Sols" UAM-CSIC and Centro de Investigación Biomédica en Red de Enfermedades Raras (CIBERER), Universidad Autónoma de Madrid 28029, Madrid, Spain ; Laboratorio de Enfermedades Mitocondriales, Instituto de Investigación Sanitaria Hospital 12 de Octubre (i+12) Madrid, Spain.
authors.forename: María Esther
authors.initials: ME
authors.lastname: Gallardo
authors.affiliation: Departamento de Bioquímica, Instituto de Investigaciones Biomédicas "Alberto Sols" UAM-CSIC and Centro de Investigación Biomédica en Red de Enfermedades Raras (CIBERER), Universidad Autónoma de Madrid 28029, Madrid, Spain ; Laboratorio de Enfermedades Mitocondriales, Instituto de Investigación Sanitaria Hospital 12 de Octubre (i+12) Madrid, Spain.
authors.forename: Miguel Ángel
authors.initials: MÁ
authors.lastname: Fernández-Moreno
authors.affiliation: Departamento de Bioquímica, Instituto de Investigaciones Biomédicas "Alberto Sols" UAM-CSIC and Centro de Investigación Biomédica en Red de Enfermedades Raras (CIBERER), Universidad Autónoma de Madrid 28029, Madrid, Spain ; Laboratorio de Enfermedades Mitocondriales, Instituto de Investigación Sanitaria Hospital 12 de Octubre (i+12) Madrid, Spain.
authors.forename: Rafael
authors.initials: R
authors.lastname: Garesse
keywords: MT-TK; Mitochondrial tRNA; pathogenicity; scoring system; trans-mitochondrial cybrid study