The genetic and phenotypic heterogeneity of neurogenetic diseases forces patients and their families into a "diagnostic odyssey." An increase in the variability of genetic disorders and the corresponding gene-disease associations suggest the need to periodically re-evaluate the significance of variants of undetermined pathogenicity. Here, we report the diagnostic and clinical utility of Targeted Gene Panel Sequencing (TGPS) and Whole Exome Sequencing (WES) in 341 patients with suspected neurogenetic disorders from centers in Buenos Aires and Cincinnati over the last 4 years, focusing on the usefulness of reinterpreting variants previously classified as of uncertain significance. After a mean of ±2years (IC 95:0.73-3.27), approximately 30% of the variants of uncertain significance were reclassified as pathogenic. The use of next generation sequencing methods has facilitated the identification of both germline and mosaic pathogenic variants, expanding the diagnostic yield. These results demonstrate the high clinical impact of periodic reanalysis of undetermined variants in clinical neurology. K E Y W O R D S diagnostic odyssey, mosaicism, targeted gene panel sequencing, variants of unknown significance, whole exome sequencing 1 | INTRODUCTION Neurogenetic diseases encompass a vast group of entities with marked genetic and phenotypic heterogeneity. Nowadays, the process of establishing a diagnosis for this subset of neurological conditions requires extensive clinical, radiological, and genetic evaluations, often becoming a "diagnostic odyssey" for the patient and the family (Carmichael, Tsipis, Windmueller, Mandel, & Estrella, 2015). Next Generation Sequencing (NGS) has become a widely used tool for obtaining genetic diagnosis in clinical medicine (Might &

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Mitochondrial diseases are multisystemic disorders characterized by an impairment of the mitochondrial respiratory chain. Diagnosis requires an approach that involves a high index of suspicion, molecular techniques and a careful selection of the tissue to be studied. Our goal was to develop and implement local strategies for diagnosing mitochondrial disorders, by standardizing procedures of molecular biology and nucleic acid sequencing. A prospective, analytical, observational study was conducted in a cohort of, a total of 82 patients with suspected mitochondrial disorder who were treated at our hospital between May 2008 and June 2019. We developed molecular diagnostic tools that included classical monogenic techniques and Next Generation Sequencing. We characterized the neurological and extra neurological manifestations noted in our cohort. Following the proposed algorithm, we obtained a molecular diagnostic performance of 54%, identifying mutations in 44 patients. mtDNA mutations were identified in 34 patients. Structural rearrangements in mitochondrial genome were found in 3 and 7 in nuclear genes, respectively. Our results confirm the utility of the proposed algorithm and the molecular tools used, as evidenced by a high diagnostic performance. This is of great value to a more efficient and comprehensive medical care of patients and families affected by mitochondrial disorders.